Protein Requirement Calculator

Grams of protein a day from weight and a published g/kg target, with the guideline named on every option — and the two options that are stated per kg of ideal weight rather than actual, which is the trap.

Last updated 8 Oct 2026

Protein requirement from a published g/kg target

Weight and a named target

Weight (kg)ACTUAL body weight for most options. The two ASPEN obesity options are stated per kg of ideal body weight, so enter the ideal weight for those — see the ideal body weight calculator. Mixing the bases is the largest error here: 2 g/kg on a 140 kg actual weight is 280 g a day where the guideline intends about 146.

Which published targetEach option carries the guideline it came from and that guideline’s figure, so the total can be audited without leaving the page. Where a guideline states a floor rather than a range, the two ends are deliberately the same number.

Which end of the published rangeBoth ends are shown below whichever is selected. For the options that state a single figure the two are identical.

84g protein/dayExample

70 kg, critically ill with a BMI under 30 (ASPEN), lower end of the range

Formula

Protein (g/day) = weight (kg) × the published target (g/kg/day)
Nitrogen (g/day) = protein (g/day) ÷ 6.25

which weight: actual body weight for every option except the two ASPEN obesity targets, which are stated per kg of ideal body weight. The guideline’s own basis governs, and this is where protein calculations most often go wrong — see ideal body weight and which weight to use
6.25: the conventional protein-to-nitrogen factor, from an assumed 16% nitrogen by mass. PENG’s Pocket Guide says to convert with 6.25 “but accept that this is just an approximation” — the true factor varies with the protein source, and crystalline amino acid mixtures differ slightly from dietary protein
a floor is not a range: ESPEN geriatrics gives “at least 1 g protein per kg body weight and day”, ESPEN’s intensive care guideline 1.3 g/kg, and ASPEN 2.0 g/kg of ideal weight for a BMI of 30 to 40. For those options the two ends of the range are the same figure, and the page says so rather than inventing an upper bound
what this does not do: it does not measure whether the protein is being retained. That is nitrogen balance, which exists as a separate calculator and depends on a complete 24-hour collection, on urine urea nitrogen rather than total nitrogen, and on an insensible-loss estimate of 2 to 4 g/day that can flip the sign of the answer near balance. Protein’s 4 kcal/g is a separate question again — see the parenteral nutrition calculator

Worked example

70 kg, critically ill with a BMI under 30 (ASPEN), lower end of the range
70 × 1.2 = 84 g protein/day; the upper end of the same range is 70 × 2.0 = 140 g/day, a range almost two-fold wide
ESPEN's intensive care guideline gives a single figure instead — 1.3 g/kg, so 91 g/day — "delivered progressively". That sits inside ASPEN's range but is not the same recommendation
Nitrogen equivalent: 84 ÷ 6.25 = 13.44 g N/day. If protein calories are counted: 84 × 4 = 336 kcal/day
Now the trap. Take a man of 178 cm weighing 140 kg — a BMI of 44.2. The ASPEN target above a BMI of 40 is 2.0 to 2.5 g/kg of ideal body weight, and his Devine ideal weight is 73.2 kg, so the target is 146 to 183 g/day
Applying the same 2.0 to 2.5 g/kg to his 140 kg actual weight gives 280 to 350 g/day — 1.9 times as much, from reading the number and not the basis
At the other end: a healthy 70 kg adult is 0.66 g/kg as the average requirement and 0.83 as the safe level — 46 to 58 g/day. The critically ill range starts above where the healthy range ends, which is the most useful thing on this page

Every target on this page, with the guideline it comes from

The weight-basis column is the one to read first: two rows are stated per kg of ideal body weight, and for a 140 kg patient at 178 cm that is a 1.9-fold difference from actual weight. Note also that the healthy adult figure and the critically ill figures do not overlap at all — illness roughly doubles the target, so a hospital patient fed to a healthy reference intake is being underfed protein by about that factor. Where ESPEN and ASPEN both address a patient they disagree: a critically ill 70 kg adult is 91 g/day by ESPEN’s recommendation 22 and 84 to 140 g/day by the ASPEN algorithm, and the overlap is only partial.
Population	Target (g/kg/day)	Weight basis	Guideline	At 70 kg (g/day)
Healthy adult	0.66 average requirement, 0.83 safe level or population reference intake	Actual	WHO/FAO/UNU 2007 and EFSA 2012, both identical	46 to 58
Older person	At least 1.0	Actual	ESPEN geriatrics 2022, recommendation 2 (Grade B, strong consensus 100%)	70
Older person with acute or chronic illness	1.2 to 1.5	Actual	PENG Pocket Guide, 5th ed	84 to 105
Critically ill	1.3 delivered progressively	Actual	ESPEN intensive care 2019, recommendation 22	91
Critically ill, BMI under 30	1.2 to 2.0	Actual	ASPEN nutrition care algorithm	84 to 140
Critically ill, BMI 30 to 40	2.0	Ideal body weight	ASPEN nutrition care algorithm	140 if 70 kg is the IDEAL weight
Critically ill, BMI 40 or more	2.0 to 2.5	Ideal body weight	ASPEN nutrition care algorithm	140 to 175 if 70 kg is the IDEAL weight
Burns	1.5 to 2.0	Actual	ESPEN and ISBI, as tabulated in PENG 2018	105 to 140
Pressure ulcer	1.25 to 1.5	Actual	NPUAP/EPUAP, as tabulated in PENG 2018	88 to 105

Protein and nitrogen, both ways, at 6.25

6.25 assumes 16% nitrogen by mass in mixed protein and is a convention rather than a measurement. It matters most in the other direction: 2 g of nitrogen, the width of the usual insensible-loss estimate in a nitrogen balance, is 12.5 g of protein a day.
Protein (g/day)	Nitrogen (g/day)	Energy if counted at 4 kcal/g
46	7.4	184 kcal
58	9.3	232 kcal
84	13.4	336 kcal
91	14.6	364 kcal
140	22.4	560 kcal

The number is easy; the weight basis is where it goes wrong

Protein targets in clinical nutrition are published as grams per kilogram per day, so the arithmetic is one multiplication. What makes the result right or wrong is almost never the multiplication: it is which guideline the figure came from, and which weight it is meant to be multiplied by.

The weight basis first, because it is the larger error. Most targets are stated on actual body weight. The ASPEN obesity targets are not: 2.0 g/kg for a BMI of 30 to 40 and up to 2.5 g/kg above 40 are both per kg of ideal body weight. For a man of 178 cm weighing 140 kg — a BMI of 44.2 — the Devine ideal weight is 73.2 kg, so 2.0 g/kg is 146 g of protein a day against the 280 g the same figure gives on actual weight: 1.9 times as much, from reading the number rather than the basis. This page therefore names the basis on every option, and the ideal body weight calculator and dosing weight interpreter cover the four weight descriptors.

Then the guideline. ESPEN’s intensive care guideline gives a single figure, 1.3 g/kg/day “delivered progressively”; the ASPEN algorithm gives 1.2 to 2.0 g/kg/day for a BMI under 30, a range almost two-fold wide. ESPEN’s geriatric guideline gives at least 1.0 g/kg/day with 100% consensus. WHO/FAO/UNU and EFSA agree on 0.66 g/kg/day as the average requirement for a healthy adult and 0.83 as the safe level, and both say older adults need at least as much as younger ones. The striking thing when these are laid side by side is the size of the step: the healthy reference intake and the critically ill targets do not overlap, so an inpatient fed to a healthy reference intake receives roughly half the protein the critical care guidelines intend.

Two boundaries. A target is not a measurement of whether protein is being retained — that is nitrogen balance, which exists as a separate calculator and carries its own difficulties: it needs a complete 24-hour collection, urine urea nitrogen is not total urinary nitrogen, renal failure invalidates the interpretation because urea accumulates instead of being excreted, and the insensible-loss term of 2 to 4 g/day is an estimate that can flip the sign of the answer near balance. Two grams of nitrogen is 12.5 g of protein, so that choice is not small. And protein and energy are separate prescriptions: the energy figure is on the resting energy expenditure calculator, and whether protein’s 4 kcal/g belongs in an energy total is a live question covered on the parenteral nutrition calculator. This page computes a figure and prints the published targets beside it with the guideline each comes from. The prescription is the clinician’s, taken with the patient in front of them.

Frequently asked questions

How much protein does a critically ill patient need?

The published targets differ. ESPEN’s 2019 intensive care guideline, recommendation 22: “1.3 g/kg protein equivalents per day can be delivered progressively”. The ASPEN nutrition care algorithm: 1.2 to 2 g/kg/day for a BMI under 30, 2 g/kg of ideal body weight for a BMI of 30 to 40, and up to 2.5 g/kg of ideal weight above that. At 70 kg actual weight those are 91 g/day and 84 to 140 g/day.

Is the protein target on actual or ideal body weight?

It depends on the target, and this is the commonest error. Most are on actual body weight; the ASPEN obesity targets — 2 g/kg for a BMI of 30 to 40 and up to 2.5 g/kg above 40 — are per kg of ideal body weight. For a man of 178 cm weighing 140 kg, whose Devine ideal weight is 73.2 kg, the difference is 1.9-fold: 146 g/day against 280.

How much protein does a healthy adult need?

WHO/FAO/UNU 2007 and EFSA 2012 both set the average requirement at 0.66 g per kg body weight per day and the safe level of intake, or population reference intake, at 0.83 g/kg/day — about 46 to 58 g/day for a 70 kg adult. Both state that older adults require at least as much as younger adults, and ESPEN’s geriatric guideline recommends at least 1.0 g/kg/day.

How do I convert protein to nitrogen?

Divide by 6.25, which assumes 16% nitrogen by mass in mixed protein: 84 g of protein is 13.44 g of nitrogen, and 13.44 g of nitrogen is 84 g of protein. The factor is a convention — PENG’s Pocket Guide says to use it “but accept that this is just an approximation”.

Does meeting the target mean the protein is being used?

No. That is nitrogen balance, a separate measurement with its own pitfalls: it needs a complete 24-hour urine collection, urine urea nitrogen is not total urinary nitrogen, renal failure invalidates the interpretation because urea accumulates rather than being excreted, and the insensible-loss term of 2 to 4 g/day can change the sign of the answer near balance — 2 g of nitrogen is 12.5 g of protein.

Related calculators

References

Singer P, Blaser AR, Berger MM, et al. ESPEN guideline on clinical nutrition in the intensive care unit. Clin Nutr. 2019;38(1):48–79. Recommendations 15 (indirect calorimetry in ventilated patients, Grade B), 17 (not exceeding 70% of energy expenditure in the early phase), 22 (1.3 g/kg protein equivalents), 23 (glucose “should not exceed 5 mg/kg/min”) and 25 (lipids “should not exceed 1.5 g lipids/kg/day”). Predictive equations are “associated with significant inaccuracy (up to 60%)”, with 20–25 kcal/kg/day named as the simplest alternative.
American Society for Parenteral and Enteral Nutrition. Nutrition Care Algorithm: critical care. 25–30 kcal/kg/day; protein 1.2–2 g/kg/day; in obesity 11–14 kcal/kg actual weight for a BMI of 30–50 and 22–25 kcal/kg ideal weight above 50, with protein 2 g/kg ideal weight for a BMI of 30–40.
Volkert D, Beck AM, Cederholm T, et al. ESPEN practical guideline: clinical nutrition and hydration in geriatrics. Clin Nutr. 2022;41(4):958–989. Recommendation 1, a guiding value of 30 kcal per kg body weight per day; recommendation 2, at least 1 g protein per kg body weight per day. Both Grade B.
European Commission, Health Promotion Knowledge Gateway. Dietary protein intake in adults. WHO/FAO/UNU 2007 and EFSA 2012 both give an average requirement of 0.66 g protein per kg body weight per day and a safe level of intake, or population reference intake, of 0.83 g/kg/day, with no higher figure for older adults.
Parenteral and Enteral Nutrition Group of the British Dietetic Association. A Pocket Guide to Clinical Nutrition. 5th ed. 2018. Replaced the factorial stress-factor method with weight-based estimation at 20–25 kcal/kg/day for a BMI of 18.5–30; activity “unlikely to exceed 20% above REE” in most hospitalised patients; nitrogen from protein using 6.25 “but accept that this is just an approximation”.

Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/