Adult Fluid Requirement Calculator: Baseline Volume and Additional Losses

A baseline maintenance volume for an adult by three named, separately sourced methods — mL per kg, 1 mL per kcal, and the tiered weight method — with pyrexia and each measured loss added as its own visible line, so you can read off what contributed what. Adults only; the paediatric case belongs to the Holliday-Segar page in the medical set.

Last updated 1 Oct 2026

These figures come from published predictive equations and reference ranges. They are not a measurement of the person in front of you, and they are not a feeding prescription — they are a starting estimate for a dietitian or clinician to weigh against the patient, the local policy and, where it is available, measurement.

Baseline maintenance volume, plus named additional losses

weight, age and measured losses → mL/day, mL/h and mL/kg/day, with the baseline shown separately

Body weight (kg)Weight in kilograms. Every method on this page is driven by weight, and all three of them behave badly at the extremes — in opposite directions, which is why the page prints all three. A flat mL/kg rate is linear for ever, so it gives 6,000 mL/day at 200 kg; the tiered method flattens out and gives 4,200 mL/day for the same person. Neither is a measurement, and at either extreme of weight the three figures below are the useful output rather than any one of them.

Age (years)Adults only; the page refuses below 18. Paediatric maintenance fluid is Holliday-Segar’s question and is answered on the paediatric maintenance fluid page in the medical set, which this page deliberately does not duplicate. Age is used here only by the optional age adjustment below, and by the note that checks the total against the geriatric drink-volume recommendation.

SexUsed for one thing only: the ESPEN geriatric guideline states its minimum daily drink volume separately for men and women, and the page checks the total against the right one of the two. None of the three volume methods on this page uses sex at all.

Baseline methodAll three are computed and shown in the rows below whichever you choose, because the gap between them is part of the answer. They are the three standards compared in Chidester and Spangler’s 1997 study of fluid intake in institutionalised older people, which is a published, citable statement of all three and is why this page uses them rather than the identical range that appears in national guidance whose licence this site cannot use.

Rate for the mL/kg method (mL/kg/day)Defaults to 30 mL/kg/day, which is the one figure in this family with a clean published statement behind it — it is “standard 1” in the 1997 Chidester and Spangler comparison. The familiar 25 to 35 mL/kg/day span is the same range arrived at a different way: water need tracks energy expenditure at about 1 mL per kcal, and an adult expending 25 to 35 kcal/kg/day therefore needs 25 to 35 mL/kg/day. The field is locked when another method is chosen, or when the age adjustment below is switched on, so the number you can see is always the number the page used.

Apply the conventional age reduction?READ THE PROVENANCE BEFORE USING THIS. The three figures are reproduced across dietetic textbooks and teaching material, and the author of this page could NOT trace them to a primary study: they are convention. What is traceable is that 30 mL/kg was applied to subjects aged 65 to 100 in the 1997 Chidester and Spangler comparison, which is the opposite of treating 30 as a middle-aged figure, and that the ESPEN geriatric guideline states a minimum drink volume in litres rather than per kilogram. The option is offered rather than hidden, switched off by default, and the page says what it is. If your unit’s figures differ, use the rate field instead and record where the number came from.

Energy expenditure for the 1 mL/kcal method (kcal/day)Only used by the 1 mL per kcal method, and locked otherwise — although the row showing what that method would give is printed whichever method is selected, so you can compare. The figure to put here is an energy estimate for the same person: the energy requirement page computes it from five published equations and prints the spread between them. The 1 mL per kcal rule goes back to Holliday and Segar’s 1957 derivation of maintenance water from caloric expenditure, which is also the origin of the paediatric 100/50/20 rule.

Body temperature (°C)Leave at 37 for no pyrexia addition. Above 37 the page adds a percentage of the baseline for each degree, using the percentage in the next field, and separately prints a much smaller alternative model so the disagreement between the two is visible rather than buried. A temperature below 37 adds nothing and subtracts nothing: there is no defensible figure for reducing a maintenance volume because somebody is cool, and inventing one would be worse than leaving it out.

Pyrexia addition (% of baseline per °C above 37)Defaults to 12.6% per °C, and the honest account of where that comes from is this: it is NOT a measurement of water loss. Basal metabolic rate rises about 7% per degree Fahrenheit of fever, a figure from the Du Bois era that is still what the textbooks print, and 7% per °F is 12.6% per °C. Combine that with water need tracking energy at 1 mL per kcal and you get an addition of about 12.6% of the baseline per °C — which is almost certainly the real origin of the “10 to 13% per °C” figure in circulation. It is a derivation through two steps, not an observation, and the row below gives the competing model for comparison. Set it to 10 if your unit uses 10, or to 0 to switch the addition off entirely.

Drain output (mL/day, measured)A measured volume off a chart, not an estimate from a table — which is why the losses on this page are entered as numbers rather than chosen from a list of conditions. Use the previous 24 hours, or the last few hours scaled up if the drain is new, and re-run the page when a fresh 24-hour figure exists. Replacing a high-volume loss is a prescribing decision about volume AND composition; this page only adds up volume.

Stoma output (mL/day, measured)Measured output from an ileostomy, jejunostomy or colostomy over 24 hours. A high-output stoma is the commonest reason a maintenance volume on this page is badly wrong, and it is also the situation where the composition of what is lost matters most — small bowel effluent carries sodium at close to plasma concentration, so replacing the volume with the wrong fluid can leave somebody euvolaemic and hyponatraemic. Volume is all this page can give you.

Vomiting or nasogastric aspirate (mL/day, measured)Measured vomit or nasogastric aspirate over 24 hours. Where vomit has not been measured, it has not been measured — putting a guess here produces a precise-looking total built on a guess, and the sensible move is to start measuring and treat the figure below as a baseline only.

Diarrhoea (mL/day, measured)Measured stool volume over 24 hours. Most wards weigh rather than measure; 1 g is taken as 1 mL, which is accurate enough for this arithmetic. If the losses you enter come to a large fraction of the total below, the page says so, because at that point the question has stopped being maintenance fluid and become replacement — a different decision with different fluids.

2,100mL/dayExample

a 40-year-old man of 70 kg, mL/kg method at 30 mL/kg/day, no age adjustment, apyrexial, no measured losses

Three baseline methods, two pyrexia models, and the losses that are simply added

mL/kg method: V_base = W × r · energy method: V_base = 1 mL × E_kcal · tiered method: V_base = 100 W for the first 10 kg, + 50 per kg to 20 kg, + 15 per kg thereafter · pyrexia: + V_base × p/100 × (T − 37) · competing pyrexia model: + 80 × (T − 38) · V_total = V_base + pyrexia + drain + stoma + vomit + stool · mL/h = V_total/24

W: body weight in kg
r: the rate in mL/kg/day. 30 is the default here because it is the figure stated as “standard 1” in the published comparison this page follows. The familiar 25–35 span is the same range reached from the other direction: 1 mL per kcal at 25–35 kcal/kg/day
E_kcal: an energy expenditure estimate in kcal/day for the same person. One millilitre of water per kilocalorie metabolised comes from Holliday and Segar’s 1957 derivation, which is also the parent of the paediatric 100/50/20 rule
100 / 50 / 15: the tiered method’s three rates. The ADULT form uses 15 mL/kg above 20 kg; the paediatric Holliday-Segar rule uses 20. Writing 20 where 15 belongs adds 250 mL/day at 70 kg
p: the pyrexia addition as a percentage of the baseline per °C above 37. Default 12.6%, which is 7% per °F — the classical figure for the rise in metabolic rate with fever — carried across to water by the 1 mL per kcal identity. It is a derivation through two steps and not a measurement of water loss, which is why the page prints a competing model beside it
80 mL/°C: the competing model: 10% of an insensible loss of about 800 mL/day, per °C above 38 °C. It is smaller than the percentage model by a factor of three or more at any realistic baseline, and it starts a whole degree later. Both are in circulation; the page shows both rather than choosing
T: body temperature in °C. Below 37 nothing is added and nothing is taken away — there is no defensible figure for reducing a maintenance volume because somebody is cool

Worked example

a 40-year-old man of 70 kg, mL/kg method at 30 mL/kg/day, no age adjustment, apyrexial, no measured losses
The baseline: 70 kg × 30 mL/kg/day = 2,100 mL/day. Nothing else has been added, so that is the headline. As an hourly rate it is 2,100/24 = 87.5 mL/h, and per kilogram it is of course 30 mL/kg/day — which is the row to watch when any of the other inputs change.
Now the same man by the other two methods, which the page prints whether or not you chose them. Tiered: 100 × 10 = 1,000 for the first 10 kg, plus 50 × 10 = 500 for the next 10, plus 15 × 50 = 750 for the remaining 50 kg, giving 2,250 mL/day. One millilitre per kilocalorie at an energy estimate of 2,000 kcal/day gives 2,000 mL/day. So the three answers are 2,000, 2,100 and 2,250 — a spread of 250 mL/day, about 12% of the smallest, for a perfectly ordinary adult. That is the honest width of this estimate before anybody is unwell.
Watch what happens at the ends of the weight range. At 200 kg the flat 30 mL/kg rate gives 6,000 mL/day and the tiered method gives 1,500 + 15 × 180 = 4,200 mL/day — a difference of 1.8 litres a day between two methods that agreed to within 250 mL at 70 kg. At 30 kg the flat rate gives 900 mL/day and the tiered method gives 1,500 + 15 × 10 = 1,650 mL/day, nearly double. Both of those gaps are the models failing, not the patient being unusual, and neither method was derived at those weights. The page prints the spread for exactly this reason.
Add a fever. At 39 °C with the default 12.6% per °C, the addition is 2,100 × 0.126 × 2 = 529 mL/day, so the total becomes 2,629 mL/day. The competing model — 80 mL per °C above 38 °C — adds 80 × 1 = 80 mL/day. The two models differ by 449 mL/day for the same patient at the same temperature, and the page shows both because a reader shown only one would have no idea the other existed. At 37.5 °C the gap is starker still: the percentage model adds 132 mL and the competing model adds nothing at all, because it does not start counting until 38.
Add measured losses. Say an ileostomy putting out 1,400 mL/day and nothing else, on the 2,100 mL baseline: the total is 3,500 mL/day, of which 40% is loss replacement. That is the point at which the page says so, because a single daily volume has stopped being the right instrument — 1,400 mL of small bowel effluent carries roughly as much sodium per litre as plasma does, so replacing it with the wrong fluid leaves somebody normovolaemic and hyponatraemic. The volume arithmetic here is correct and is also not the hard part.
What this page will not do. It will not tell you what to prescribe, what to prescribe it as, or whether to prescribe anything: no fluid status, no sodium, no potassium, no renal or cardiac function, no restriction, and no account of what has already gone in. It also has no paediatric branch, deliberately — the paediatric maintenance fluid page owns Holliday-Segar and this page refuses under 18 rather than extending an adult method into childhood. For what has actually gone in and come out, use the fluid balance chart page, and for the energy figure that is prescribed alongside this volume, the energy requirement page.

The three baseline methods across the adult weight range

The third column assumes an energy expenditure of 30 kcal/kg/day, which makes it numerically identical to the flat 30 mL/kg column — that is the point, and it is why the 25–35 mL/kg span and the 1 mL per kcal rule are the same statement wearing different clothes. The interesting column is the tiered one. It crosses the flat rate at exactly 80 kg and diverges in both directions, because 15 mL/kg above 20 kg is a lower marginal rate than 30 mL/kg while the first 20 kg are charged at far more. At 30 kg the two methods differ by 83% of the smaller figure, and at 200 kg by 43%. Neither is a measurement; both are models of obligatory loss, and outside roughly 60–100 kg they stop agreeing enough for either to be quoted alone.
Body weight	Flat 30 mL/kg/day	Tiered 100/50/15	1 mL per kcal at 30 kcal/kg	Widest gap
30 kg	900 mL	1,650 mL	900 mL	750 mL (83%)
45 kg	1,350 mL	1,875 mL	1,350 mL	525 mL (39%)
60 kg	1,800 mL	2,100 mL	1,800 mL	300 mL (17%)
70 kg	2,100 mL	2,250 mL	2,100 mL	150 mL (7%)
80 kg	2,400 mL	2,400 mL	2,400 mL	0 mL (0%)
100 kg	3,000 mL	2,700 mL	3,000 mL	300 mL (11%)
150 kg	4,500 mL	3,450 mL	4,500 mL	1,050 mL (30%)
200 kg	6,000 mL	4,200 mL	6,000 mL	1,800 mL (43%)

The two pyrexia models, at a 2,100 mL/day baseline

Both of these are in circulation and they are not close. The percentage model is the “10 to 13% per °C” figure that appears in dietetic and nursing material; it is best understood as the classical rise in metabolic rate with fever (about 7% per °F, so 12.6% per °C) carried across to water by the 1 mL per kcal identity, which means it is a derivation through two steps rather than a measurement of water loss. The insensible-loss model takes 10% of an insensible loss of roughly 800 mL/day for each °C above 38 °C, which is 80 mL/°C and starts a whole degree later. The author of this page could not find a primary measurement of water loss per degree of fever in an adult that supports either figure, and says so rather than picking one and looking confident. If the fever is large enough for the difference to matter, measure the balance.
Temperature	Percentage model (12.6% of baseline per °C above 37)	Insensible-loss model (80 mL per °C above 38)	Ratio
37.0 °C	0 mL	0 mL	—
37.5 °C	132 mL	0 mL	no comparison — the second model has not started
38.0 °C	265 mL	0 mL	no comparison — the second model has not started
39.0 °C	529 mL	80 mL	6.6×
40.0 °C	794 mL	160 mL	5.0×
41.0 °C	1,058 mL	240 mL	4.4×

Where each number on this page comes from

This table exists because a fluid calculator is almost entirely made of numbers whose origin nobody states. Three of the figures above are published methods that can be cited cleanly; two are derivations from published statements and are labelled as derivations; one — the age reduction — could not be traced at all and is offered switched off, with that written next to it. The one national guideline that carries the familiar range is deliberately not used anywhere on this page, for licensing reasons set out in the row for it.
Figure	Source used	What was rejected or could not be established
30 mL/kg/day baseline	Chidester JC, Spangler AA, J Am Diet Assoc 1997;97(1):23–8, which states 30 mL/kg body weight as “standard 1” of three established standards it compares. A peer-reviewed statement of the method, freely citable.	NICE CG32 also carries the 25–35 mL/kg/day range. It is not used, and no part of this page is built on it: the NICE UK Open Content Licence is UK-only and forbids display of the licensed information next to advertising, and this site carries advertising.
The 25–35 mL/kg/day span	Derived here rather than quoted: water need tracks energy at 1 mL per kcal (Holliday & Segar 1957), and an adult expending 25–35 kcal/kg/day therefore needs 25–35 mL/kg/day. An arithmetic consequence of two sourced statements, not a reproduction of anybody’s table.	Nothing had to be rejected, but it is worth being explicit that this is a derivation. The span is extremely widely printed and almost never sourced.
1 mL per kcal	Holliday MA, Segar WE, The maintenance need for water in parenteral fluid therapy, Pediatrics 1957;19:823–32 — the derivation of maintenance water from caloric expenditure, about 100 mL per 100 kcal metabolised. Also “standard 2” in the 1997 comparison above.	—
Tiered 100 / 50 / 15 mL/kg	“Standard 3” in Chidester & Spangler 1997, stated as 100 mL/kg for the first 10 kg, 50 mL/kg for the next 10 kg and 15 mL for each remaining kg — the ADULT form.	The paediatric Holliday-Segar form uses 20 mL/kg for the remainder, not 15. Mixing the two is a 5 mL/kg/day error across most of an adult’s weight, and it is a common one.
Age reduction 35 / 30 / 25 mL/kg	Nothing citable. These figures are reproduced across dietetic textbooks and teaching material and could not be traced to a primary study. They are offered on this page as an OPTION, switched off by default, with that stated.	A primary source. None was found. Note also that the 1997 comparison applied 30 mL/kg to subjects aged 65 to 100, which does not sit comfortably with 30 being a middle-aged figure and 25 an elderly one.
Minimum 2.0 L men, 1.6 L women	ESPEN guideline on clinical nutrition and hydration in geriatrics (Volkert et al.), a grade B recommendation on daily drink volume for older people. Cited by recommendation and figure, not reproduced as text.	This is a drinks figure rather than a total fluid figure, so it is used as a floor to flag against rather than as a method. It is not a per-kilogram statement and should not be turned into one.
Pyrexia 12.6% per °C	A derivation stated as such: about 7% rise in metabolic rate per °F of fever, the classical Du Bois-era figure still printed in nutrition textbooks, which is 12.6% per °C; combined with 1 mL per kcal.	A primary measurement of water loss per degree of fever in adults. None was found. The commonly quoted “10 to 13% per °C” appears to be this derivation rather than an observation, and the page says so.
Insensible loss about 800 mL/day	Brandis K, Fluid Physiology, section on insensible water loss: minimal insensible loss in an adult about 800 mL/day, roughly 400 mL from skin and 400 mL from respiration. Used only to scale the competing pyrexia model. A separate parenteral-nutrition teaching source puts adult insensible loss at 800–1,100 mL/day, which is consistent.	The 50 mL/h figure quoted alongside it in the same source is attributed only to “has been suggested”, so it is not used here.
Drain, stoma, vomit and stool volumes	Not sourced and not modelled — they are measurements the reader enters. This is the only part of the page that is about the patient in front of you rather than about a population.	Every published table of “typical” output volumes by condition. None is used: a guessed loss produces a precise-looking total built on a guess.

A baseline is not a prescription: what each of these three methods is actually a model of

A maintenance fluid volume answers a narrow question: how much water does an adult lose when nothing in particular is wrong? Urine that carries the day’s solute load, water lost through skin and breath, a little in stool. Add those up and you have an obligatory loss, and a volume that replaces it is a maintenance volume. Everything else — a deficit, a third space, a high-output stoma, heart failure, a restriction, what has already gone in since midnight — sits outside that question, and this page does not pretend to answer any of it. What it does is compute the baseline by three named methods, add the losses you have actually measured as separate visible lines, and print the gap between the methods so that the width of the estimate is on the screen rather than in a footnote.

The three methods are three different models of the same obligatory loss, and they only agree in the middle. A flat rate in mL/kg/day is linear: it assumes loss scales with body mass for ever, which it does not, and at 200 kg it produces six litres a day. The tiered method — 100 mL/kg for the first 10 kg, 50 for the next 10, 15 for the rest — charges the first 20 kg heavily and then flattens, which is a better shape, and it gives 4.2 litres for the same 200 kg person. The two cross at exactly 80 kg and diverge in both directions; at 30 kg they differ by 83% of the smaller figure. The third method ties fluid to energy at one millilitre per kilocalorie, which is the most physiologically direct of the three because water loss really does track metabolic rate, and which inherits all the uncertainty of the energy estimate it is given. None of them is a measurement. Quoting one of them alone, to the nearest 50 mL, is false precision of a kind this subject is full of.

Where the familiar 25 to 35 mL/kg/day comes from, and why this page sources it the way it does. That span appears in national guidance that this site cannot build on: the NICE UK Open Content Licence is restricted to the United Kingdom and expressly does not permit the licensed information to be displayed next to advertising, and this site carries advertising. So the range is sourced here two other ways instead. The single figure of 30 mL/kg is stated as one of three established standards in a 1997 peer-reviewed comparison of fluid intake in institutionalised older people, which also states the 1 mL per kcal rule and the tiered method — all three of this page’s methods come from that one citable place. And the span itself falls out arithmetically: water need tracks energy at about 1 mL per kcal, a relationship Holliday and Segar set out in 1957 when they derived maintenance water from caloric expenditure, so an adult expending 25 to 35 kcal/kg/day needs 25 to 35 mL/kg/day. The two ranges are the same statement. That is worth knowing in its own right, because it means a fluid target and an energy target are not independent numbers to be checked against each other — one is largely a restatement of the other.

The age adjustment is the weakest content on this page and it is switched off by default. Requirement per kilogram is widely said to fall in older adults, and the figures usually given are 35 mL/kg up to about 55, 30 from 56 to 65, and 25 above 65. Those three numbers are reproduced across dietetic textbooks and teaching material, and no primary study could be found behind them. They are convention. They are offered here as an explicit option, labelled as convention, rather than applied silently — and two things sit awkwardly beside them. The 1997 comparison applied 30 mL/kg to subjects aged 65 to 100, treating 30 as the figure FOR older people rather than for the middle-aged. And the ESPEN geriatric guideline does not give a per-kilogram figure at all: it gives absolute minimum drink volumes, at least 2.0 litres a day for men and 1.6 for women, as a grade B recommendation. The physiology pulls both ways — total body water and lean mass fall with age, which lowers the requirement, while renal concentrating ability and the thirst response also fall, which raises the consequence of getting it wrong — and the honest summary is that there is no clean per-kilogram answer for an older adult. The page therefore flags the total against the absolute floor, which is a figure somebody published, and leaves the per-kilogram reduction as an option you have to choose.

Pyrexia: two models, a factor of three or more apart, and no primary measurement behind either. The commonly quoted figure is a 10 to 13% increase in fluid requirement for each degree Celsius above 37. Trace it back and it is not a measurement of water loss: it is the classical figure for the rise in metabolic rate with fever — about 7% per degree Fahrenheit, which is 12.6% per degree Celsius — carried across to water by the 1 mL per kcal identity. That is a coherent derivation through two sourced steps, and this page uses it as the default while saying exactly that. The competing figure, from paediatric fluid teaching, adds 10% of the insensible loss for each degree above 38 °C; with adult insensible loss at roughly 800 mL/day that is 80 mL per degree, it starts a whole degree later, and at 39 °C on a 2,100 mL baseline the two models give 529 mL and 80 mL. No primary measurement of adult water loss per degree of fever was found that supports either. Both are printed, with the gap between them, because a reader shown one number would reasonably assume it was the number.

Measured losses are the only figures here about the patient in front of you. Drain, stoma, vomit or nasogastric aspirate and stool are entered as measured millilitres from the chart, not chosen from a table of typical volumes, because a guessed loss produces a precise-looking total built on a guess. Each appears on its own row so the total can be read back, and when they come to more than 40% of the total the page says so — at that point the question has changed from maintenance to replacement, and replacement is about composition as well as volume. Small bowel and stoma effluent carries sodium at close to plasma concentration; gastric aspirate carries hydrogen and chloride; stool in high-output diarrhoea carries potassium and bicarbonate. Replacing the right volume with the wrong fluid is a recognised way to leave somebody normovolaemic and badly deranged, and the volume arithmetic on this page is both correct and not the hard part of that problem.

Adults only, deliberately. There is no paediatric branch and the page refuses an age under 18 rather than extending an adult method into childhood: the paediatric maintenance fluid page owns the Holliday-Segar calculation, including the 4-2-1 hourly form, and duplicating it here would mean two pages that could disagree. For what has actually gone in and come out over a shift, use the fluid balance chart page; for urine output per kilogram per hour, the urine output page. The energy figure prescribed alongside this volume, and the one to put into the 1 mL per kcal method, comes from the energy requirement page; the water a feed itself carries, which counts towards this total and is easy to forget, is on the enteral feed rate page. Refeeding risk is assessed on the hypophosphataemia and refeeding risk interpreter and is not reproduced here.

Frequently asked questions

Why does this page not just give me 25 to 35 mL/kg/day?

Because that range is a conclusion rather than a method, and because the guidance it is most often quoted from cannot be used on this site: the NICE UK Open Content Licence is limited to the United Kingdom and does not permit the licensed information to be displayed alongside advertising, which this site carries. So the page gives you the three methods that range summarises, each from a source it can cite, and lets you see them disagree. It also shows where the range comes from: water need tracks energy at about 1 mL per kcal, and an adult expending 25 to 35 kcal/kg/day therefore needs 25 to 35 mL/kg/day. If you want the familiar answer, set the rate to 30 and read the headline; the default does exactly that.

Which of the three methods should I use?

Whichever your local policy names, so that your figures are comparable with your colleagues’. Beyond that, the three have different failure modes and the table on this page shows them. A flat mL/kg rate is the simplest and is reasonable between roughly 60 and 100 kg, where all three agree to within about 10%; it overestimates badly in a very heavy adult and underestimates in a very light one. The tiered method has a better shape at the extremes because it charges the first 20 kg heavily and then flattens. The 1 mL per kcal method is the most physiologically direct and the right choice when you already have an energy estimate you believe, since it ties the two targets together explicitly rather than leaving them to be reconciled. What you should not do is take one number from one method and quote it to the nearest 50 mL.

Where do the age-banded figures come from?

Nowhere that could be verified, which is why they are an option switched off by default rather than something the page applies silently. The figures 35 mL/kg up to 55, 30 from 56 to 65 and 25 above 65 are reproduced widely in dietetic textbooks and teaching material, and no primary study behind them could be found. Two things complicate them further. The 1997 comparison that this page’s methods come from applied 30 mL/kg to subjects aged 65 to 100 — that is, as the figure for older people. And the ESPEN geriatric guideline gives absolute minimum drink volumes, at least 2.0 litres a day for men and 1.6 for women, rather than any per-kilogram figure. The page flags the total against that floor because it is a published number, and leaves the per-kilogram reduction as a choice you have to make deliberately.

Is the fever figure 10% per degree, 13% per degree, or a flat volume?

All three are in circulation and none of them could be traced to a primary measurement of water loss in adults. The percentage figure is best understood as a derivation: metabolic rate rises about 7% per degree Fahrenheit of fever, which is 12.6% per degree Celsius, and water need tracks energy at about 1 mL per kcal, so the water requirement rises by roughly the same percentage. That is the default on this page and it is labelled as a derivation. The flat-volume figure comes from a different model that adds 10% of the insensible loss — about 800 mL/day in an adult — for each degree above 38 °C, giving 80 mL per degree. At 39 °C on a 2,100 mL baseline the two give 529 mL and 80 mL. The page prints both and the gap between them, and if the fever is large enough for that gap to matter, the answer is to measure the balance rather than to choose a model.

Why are the losses typed in rather than chosen from a list?

Because they are measurements and the rest of the page is models. A drain, a stoma, an aspirate and a stool chart all produce real millilitres, and a table of typical volumes by condition would replace a measurement with an average and then present the total to the nearest millilitre. If a loss has not been measured, it has not been measured: put 0 in, read the baseline, and start measuring. The page shows each loss on its own row and flags when they exceed 40% of the total, because past that point the calculation is replacement rather than maintenance, and replacement depends on what is in the fluid being lost as much as on how much of it there is.

Does the page handle children?

No, and that is deliberate rather than an omission. It refuses an age under 18. Paediatric maintenance fluid is Holliday and Segar’s calculation — 100 mL/kg for the first 10 kg, 50 for the next 10 and 20 for the rest, or the 4-2-1 rule per hour — and it is answered on the paediatric maintenance fluid page in the medical set. Two pages doing the same arithmetic is two pages that can disagree, so this one does not. Note the one-digit difference that makes the paediatric and adult tiered methods different calculations: 20 mL/kg above 20 kg for a child, 15 for an adult.

Is 6,000 mL/day really right for somebody of 200 kg?

It is what a flat 30 mL/kg/day rate gives, and that is the point at which the method should stop being used rather than the point at which you prescribe six litres. The tiered method gives 4,200 mL for the same person, 1.8 litres less, and neither method was derived in people of that weight. The page prints the spread and flags weights above 120 kg for that reason. In practice volumes at this end are usually capped, and which cap to apply is a prescribing decision that depends on cardiac and renal function, not an arithmetic one. The same caution runs the other way: at 30 kg the flat rate gives 900 mL/day, which is below the absolute floor that geriatric guidance describes for an older adult, and the page flags that too.

Why does the total in mL/h matter?

Because a daily volume has to be delivered at a rate, and the hourly figure is the one that goes on a pump or a chart. The page divides by 24, which assumes the volume runs continuously over a full day; if it is to be given over a shorter period, the hourly rate is higher in proportion and that arithmetic belongs on the infusion pages rather than here. It is also a useful sanity check in its own right: an adult maintenance volume usually lands somewhere between about 60 and 125 mL/h, and a figure well outside that is worth a second look at the inputs before anything is programmed.

Related calculators

References

Chidester JC, Spangler AA. Fluid intake in the institutionalized elderly. J Am Diet Assoc 1997;97(1):23–8. The source used for all three baseline methods on this page, which it sets out as three established standards: 30 mL/kg body weight (standard 1); 1 mL/kcal of energy consumed (standard 2); and 100 mL/kg for the first 10 kg, 50 mL/kg for the next 10 kg and 15 mL for each remaining kg (standard 3). Chosen deliberately as a freely citable peer-reviewed statement of the methods. Note that it applied these standards to subjects aged 65 through 100, which is relevant to the age-band question discussed on this page.
Holliday MA, Segar WE. The maintenance need for water in parenteral fluid therapy. Pediatrics 1957;19(5):823–32. The primary derivation of maintenance water from caloric expenditure — about 100 mL of water per 100 kcal metabolised, hence 1 mL per kcal — and the origin of the tiered 100/50/20 rule and its 4-2-1 hourly form. Cited here for the 1 mL per kcal identity, which is also the bridge used to derive the 25–35 mL/kg/day span and the percentage pyrexia model. The paediatric application of this paper is covered on the paediatric maintenance fluid page, not here.
Volkert D et al. ESPEN guideline on clinical nutrition and hydration in geriatrics. Clin Nutr 2019. Cited for its grade B recommendation on daily drink volume in older people — at least 1.6 L a day for women and 2.0 L for men, unless a clinical condition requires otherwise — which this page uses as an absolute floor to flag the total against. The recommendation is cited by its figures and its grade; no guideline text or table is reproduced, because ESPEN guidelines are copyrighted.
Brandis K. Fluid Physiology, chapter 3, section on insensible water loss (available as an open text under CC BY-NC-SA). Minimal insensible loss in an adult about 800 mL/day, roughly 400 mL from skin and 400 mL from respiration. Used on this page only to scale the competing pyrexia model (10% of 800 mL per °C = 80 mL/°C). The 50 mL/h figure the same source quotes for unstressed hospitalised patients is attributed there only to “has been suggested” and is therefore not used.
Fessler TA. Fluid and Electrolytes in Adult Parenteral Nutrition (continuing-education monograph, Today’s Dietitian). Cited as an independent cross-check on two figures: adult insensible losses of approximately 800 to 1,100 mL/day, which brackets the 800 mL used above, and about 300 mL/day of water generated by oxidation of carbohydrate, protein and fat — a term none of the three methods on this page accounts for explicitly, and a reminder that all of them are approximations of a balance rather than a balance.
University of Texas Medical Branch paediatric core curriculum, fluid and electrolyte therapy sections on normal maintenance requirements and maintenance requirements in disease. Cited for two things only: an independent statement of the 1 mL per kcal relationship (100 mL of fluid per 100 kcal burned), and the competing pyrexia model in the form this page implements it — add 10% to the transcutaneous loss replacement for every degree above 38 °C. Worth recording that this second figure applies the 10% to the INSENSIBLE component and starts at 38 °C, which is a materially smaller and later claim than applying 10 to 13% to the whole requirement from 37 °C upward. Both forms are in circulation and this page shows both.
Metabolic rate and fever: the classical figure is a rise of about 7% in basal metabolic rate for each degree Fahrenheit of body temperature, which is 12.6% per degree Celsius. It is a Du Bois-era observation and is still what current nutrition textbooks print (for example DeBruyne, Whitney & Pinna, Nutrition and Diet Therapy, 2007, p. 150). This page uses it, combined with 1 mL per kcal, as the stated derivation behind its default 12.6% per °C pyrexia addition. PROVENANCE NOTE: no primary measurement of adult WATER loss per degree of fever was found in preparing this page. The widely quoted “10 to 13% per °C” fluid figure appears to be this metabolic observation carried across by the 1 mL per kcal identity rather than an observation of water loss, and the page states that rather than presenting the figure bare.
Licensing position taken for this page, recorded deliberately because it determined the sources above. The 25–35 mL/kg/day range appears in NICE CG32. No part of this page is built on NICE text, criteria or tables: the NICE UK Open Content Licence is restricted to the United Kingdom and states that the licensed information may not be displayed next to advertising, and calcengines.com carries advertising. The range is therefore sourced instead to Chidester & Spangler 1997 for the 30 mL/kg figure and derived from Holliday & Segar 1957 for the span. ESPEN guideline content is cited by recommendation and figure, not reproduced. No criteria list appears anywhere on this page; refeeding risk criteria in particular are deliberately absent and are covered on a separate interpreter page.
Derivations performed for this page rather than taken from a source, recorded so they can be checked. (1) The tiered adult method crosses a flat 30 mL/kg/day rate at exactly 80 kg: 1,500 + 15(W − 20) = 30W gives 1,200 = 15W, W = 80. (2) At 200 kg the flat rate and the tiered method differ by 1,800 mL/day, and at 30 kg by 750 mL/day — 83% of the smaller figure — so the two methods agree only over roughly the middle of the adult weight range. (3) The 1 mL per kcal method is numerically identical to a flat mL/kg rate whenever the energy estimate equals that rate times weight, which is why the 25–35 mL/kg span and the 1 mL per kcal rule are the same statement. (4) Writing 20 mL/kg instead of 15 in the tail of the tiered method adds 5 mL/kg/day for every kilogram above 20, which is 250 mL/day at 70 kg.

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