Infusion Pump Rate Calculator: mL per Hour

The mL/h to set on the pump for a dose already prescribed in mcg/kg/min, mg/kg/h, units/kg/h or a flat rate — with the concentration, the dose read back in several units so a factor of sixty or a thousand cannot hide, how long the bag lasts, and the dose a pump already running is actually delivering.

Last updated 1 Oct 2026

This calculates a rate or a volume from a prescription that has already been written. It does not decide what to give. Check every figure against the prescription and your local policy, and have it independently checked before administration.

Pump rate in mL/h

prescribed dose, weight, bag strength → mL/h, and the dose read back

Patient weight (kg)The weight the prescription is written against. Whether that is actual, ideal or adjusted body weight is a prescribing decision, not an arithmetic one — see the dosing weight page. Ignored entirely when the dose units below are a flat rate rather than a per-kilogram one.

Prescribed dose — the numberJust the number from the prescription. Its units go in the box below, and they must be the units the prescription is actually written in — not the units you are used to.

… and the units it is prescribed inRead this off the prescription, slowly. mcg/kg/min and mcg/kg/h differ by a factor of sixty and nothing else; mcg and mg differ by a factor of a thousand. Those are the two mistakes this page exists to make visible, and they are why the dose is printed back below in five different units: if the read-back does not show the number that was prescribed, something above is wrong.

Drug in the bag or syringe — the amountThe TOTAL amount of drug in the bag or syringe once it is made up, not the amount in one ampoule and not a concentration. If the bag was made up from vials, work out what went in first — the C1V1 = C2V2 dilution page covers the dilution arithmetic.

… and the units that amount is inAlmost always mg on a printed label, but read it. A dose prescribed in units (heparin, insulin) can only be worked out from a bag labelled in units, and a dose prescribed as a mass can only be worked out from a bag labelled as a mass. Mix the two and the page refuses to answer rather than inventing a conversion that does not exist.

Volume in the bag or syringe (mL)The FINAL volume once the drug has been added, which is what the pump will deliver. If 20 mL of drug went into a 250 mL bag, the final volume is 270 mL unless an equal volume was removed first — and whether it was is a question about how the bag was made up, so check rather than assume.

Rate the pump is already running at (mL/h)Leave at 0 unless you are checking a running infusion. Put in the rate on the pump screen and the page works out the dose the patient is actually receiving — the handover question.

Total the drug and volume over this many hours (h)Used only for the running-total rows: the volume infused, the drug given and the number of bags needed over the period you name. 24 is the usual answer to “how many bags will I need for the shift”.

13.13mL/hExample

Dopamine 400 mg in 250 mL, a 70 kg patient, prescribed 5 mcg/kg/min, totalled over 24 hours

From a prescribed dose to mL/h, and back again

C = A/V · D_canon = D × k × (W if per kg) · rate = D_canon/C · dose = rate × C / (k × W) · mcg/kg/min → mL/h: rate = D × W × 60 × V / (A_mg × 1000)

A, V, C: the total drug in the bag, the final volume in mL, and the concentration A/V. Everything on this page turns on the concentration and nothing else about the bag matters — 400 mg in 250 mL and 800 mg in 500 mL are the same infusion and give the same rate
k: the one multiplier that reduces every prescribed dose unit to canonical units per hour. 60 for a per-minute order (minutes in an hour), 1000 for an order in milligrams against a bag read in micrograms, 60000 for mg/kg/min where both apply, and 1 for mcg/kg/h and units/kg/h, which are already per hour. This is where a factor of sixty or a thousand hides, and it is the only place it can hide
W: weight in kg, applied only when the prescription is per kilogram. For a flat order in mg/h or mcg/min the weight does not enter the rate at all
mcg/kg/min → mL/h: the case worth writing out, because it crosses both conversions at once. rate = D × W × 60 / C_mcg/mL, and with the bag read in mg, C_mcg/mL = 1000 A_mg/V. So rate = 60 D W V / (1000 A_mg) = 0.06 D W V / A_mg. The 60 and the 1000 do NOT cancel; they combine into 0.06, which is why the hand formula is written “× 60 ÷ 1000”
units: a unit of heparin or insulin is an activity defined against a reference standard, not a weight. There is no k that converts units to milligrams, so a dose in units and a bag in milligrams have no answer and this page returns none

Worked example

Dopamine 400 mg in 250 mL, a 70 kg patient, prescribed 5 mcg/kg/min, totalled over 24 hours
The concentration first, because every step after this uses it and nothing else about the bag matters: 400 mg in 250 mL = 1.6 mg/mL, which is 1,600 mcg/mL. Look at that number and check it against the bag in your hand before going on.
Now the dose, reduced to one canonical rate. 5 mcg/kg/min × 70 kg = 350 mcg per minute. The pump is set per hour, so × 60 = 21,000 mcg per hour. That is the factor of sixty, and it is the whole of it.
Divide the dose per hour by the concentration and the micrograms cancel, leaving mL per hour: 21,000 mcg/h ÷ 1,600 mcg/mL = 13.125 mL/h.
Where the thousand comes in: the bag was labelled in MILLIGRAMS and the dose in MICROGRAMS. Written in one line with the bag in mg, rate = 5 × 70 × 60 × 250 / (400 × 1000) = 5,250,000/400,000 = 13.125. The 60 and the 1000 do not cancel — they combine into the 0.06 that hand formulas write as "× 60 ÷ 1000". Had the bag amount been entered as 400 micrograms instead of 400 mg, the answer would have been 13,125 mL/h, which is why this page puts a red band on anything above 500.
Set it on the pump: 13.1 mL/h if it takes a decimal, 13 mL/h if it does not. At 13 mL/h the patient actually receives 13 × 1,600/60/70 = 4.95 mcg/kg/min rather than 5, which is 99.05% of the prescription. At 13.1 it is 4.99. Both are fine for dopamine and neither is 5.
READ IT BACK. The page prints 5.0000 mcg/kg/min, 300 mcg/kg/h, 0.3 mg/kg/h and 21 mg/h, which are all the same prescription in different clothes. That read-back is the only defence against a wrong unit choice, because every wrong choice on this page still produces a plausible-looking rate: had "mcg/kg/h" been picked instead of "mcg/kg/min", the answer would have been 0.22 mL/h and the read-back would have shown 0.0833 mcg/kg/min instead of 5.
The bag: 250 mL at 13.125 mL/h lasts 19.05 hours, so a little over one bag covers a 24-hour period — 1.26 bags, 315 mL and 504 mg of dopamine over the day.
Three independent sources reproduce this arithmetic exactly and are listed in the references: Nipride 50 mg in 250 mL at 0.5 mcg/kg/min for an 81.8 kg patient gives 12.27 mL/h; propofol at 15 mg/mL and 30 mcg/kg/min for 75 kg gives exactly 9 mL/h; and heparin 25,000 units in 250 mL at 18 units/kg/h gives 7 mL/h at 40 kg and 31 mL/h at 170 kg, matching a published health-service nomogram row for row.

The same delivery, written seven ways — all 13.125 mL/h

Seven ways of writing one prescription, all reducing to 21,000 micrograms an hour and therefore to one pump rate. The point of the table is that the conversion is exact and the page is not approximating anything: if you enter the same prescription in any of these forms you get the same rate to the last decimal. The point of SHOWING it is the opposite — these seven numbers are 5, 300, 0.005, 0.3, 350, 21000 and 21, and picking the wrong row for the number in front of you is how an infusion goes wrong by a factor of sixty or a thousand.
Prescription as written	Dose per hour for a 70 kg patient	Rate from a 400 mg in 250 mL bag
5 mcg/kg/min	21,000 mcg/h	13.125 mL/h
300 mcg/kg/h	21,000 mcg/h	13.125 mL/h
0.005 mg/kg/min	21,000 mcg/h	13.125 mL/h
0.3 mg/kg/h	21,000 mcg/h	13.125 mL/h
350 mcg/min (flat)	21,000 mcg/h	13.125 mL/h
21,000 mcg/h (flat)	21,000 mcg/h	13.125 mL/h
21 mg/h (flat)	21,000 mcg/h	13.125 mL/h

What a wrong entry actually does — measured, not asserted

Measured rather than asserted. Each slip was applied across ten weights from 2 to 150 kg, ten doses from 0.01 to 50 mcg/kg/min and twelve bag strengths from 1 mg in 50 mL to 1.6 g in 250 mL, keeping the 532 combinations in which the CORRECT rate falls in the normal band — the only cases where a slip has anywhere to hide. Two uncomfortable conclusions. First, the rate band is a reliable detector of a thousand-fold mass error and of almost nothing else: four of these nine slips stay inside the normal band most of the time, including the flat mg/h mix-up, which survives three times in four. Second, the two check rows are complementary and neither is sufficient on its own — a wrong dose unit moves the read-back, a wrong bag unit or volume moves the concentration, and the read-back stays self-consistent with a wrong bag volume. Between them they caught eight of the nine slips in every single case. The ninth is a wrong weight, which changes the rate, leaves the concentration correct and leaves the read-back reading back exactly the dose that was prescribed. That is the field to check by hand.
Prescription says	But you pick or type	The rate moves by	Does the rate band catch it?	What does catch it
mcg/kg/min	mg/kg/min	× 1,000	Always — 0 of 532 stayed in the normal band	The band, and the READ BACK rows
Bag amount in mg	mcg	rate × 1,000	Always — 0 of 532	The band, and the CONCENTRATION rows
Bag amount in mg	g	rate ÷ 1,000	Always — 0 of 532	The band, and the CONCENTRATION rows
mcg/kg/min	mcg/kg/h	÷ 60	Usually — 43 of 532 stayed in the normal band	The READ BACK rows, in every case tested
mcg/kg/min	mg/kg/h	× 16.7, which is 1,000/60	NO — 220 of 532 stayed in the normal band	The READ BACK rows, in every case tested
mcg/kg/min	mcg/min, flat	÷ the weight	NO — 130 of 532 stayed in the normal band	The READ BACK rows, in every case tested
mcg/kg/min	mg/h, flat	× 1,000/(60 × weight)	NO — 403 of 532 stayed in the normal band	The READ BACK rows, in every case tested
250 mL in the bag	25 mL typed	÷ 10	NO — 304 of 532 stayed in the normal band	The CONCENTRATION rows. The READ BACK rows do NOT — they stay self-consistent with the wrong volume
70 kg	7 kg typed	÷ 10	NO — 351 of 532 stayed in the normal band	NOTHING ON THIS PAGE. Read the weight back off the prescription

Doses in units: why no milligram figure is offered

A unit of heparin or insulin measures biological activity against a reference standard; a milligram measures mass. The relationship between them is a property of the particular preparation and is not a conversion factor anyone should type into a calculator. When the dose family and the bag family do not match, this page returns no answer at all and says why. That is deliberate: a wrong answer here would look exactly like a right one.
Preparation	How it is prescribed	How the bag is labelled	Does this page answer?
Unfractionated heparin	units/kg/h or units/h	units	Yes
Soluble insulin	units/h	units	Yes
Unfractionated heparin	units/kg/h	mg	No — it refuses
Any drug prescribed by mass	mcg/kg/min, mg/h	mg, mcg or g	Yes
Any drug prescribed by mass	mcg/kg/min	units	No — it refuses

Where the factor of sixty and the factor of a thousand live

A pump is set in millilitres per hour and a prescription is almost never written that way. It is written as a dose: so many micrograms per kilogram per minute, so many units per kilogram per hour, so many milligrams per hour. Getting from one to the other needs the concentration of the bag and, usually, two unit conversions — one of time and one of mass. This page does that conversion and nothing else. It does not decide what the dose should be, and it will not tell you.

The whole calculation is three lines. Work out the concentration, C = A/V, where A is the total drug in the bag and V is the final volume. Work out the dose per hour: the prescribed number, multiplied by the weight if the order is per kilogram, multiplied by 60 if the order is per minute, multiplied by 1000 if the order is in milligrams while the concentration is in micrograms. Divide the second by the first and the drug units cancel, leaving mL per hour. That is it. Everything else on the page is a cross-check on those three lines.

The dangerous case is mcg/kg/min, because it crosses both conversions at once. Dopamine 400 mg in 250 mL, 5 mcg/kg/min, 70 kg. The dose is 350 micrograms a minute, which is 21,000 micrograms an hour: that is the 60. The bag is 1.6 milligrams per millilitre, which is 1,600 micrograms per millilitre: that is the 1000. 21,000 divided by 1,600 is 13.125 mL/h. Written as one expression with the bag in milligrams, rate = dose × weight × 60 × volume / (amount × 1000), and the 60 and the 1000 do not cancel — they combine into 0.06. A page that dropped the 60 would say 0.22 mL/h and a page that dropped the 1000 would say 13,125; both are wrong by a margin that a tired reader at three in the morning may not catch, which is why this page prints the dose back in five different units underneath the answer.

Two check rows, and one entry that nothing can check. Every wrong unit choice on this page produces an arithmetically perfect, plausible-looking rate, so the page carries two rows whose only purpose is to be compared against something outside it. The rows marked READ BACK give the dose the calculated rate delivers, in mcg/kg/min and four other units: compare them with the prescription. The CONCENTRATION rows give the strength of the bag in mg/mL and mcg/mL: compare them with the label in your hand. The two are complementary rather than redundant, and that is the point. A wrong dose unit moves the read-back and leaves the concentration untouched. A wrong bag unit, or a bag volume with its decimal point in the wrong place, moves the concentration and leaves the read-back untouched — because the read-back stays perfectly self-consistent with whatever was typed, which is exactly why one row on its own is not enough. Do not rely on the band to catch a unit error. Sweeping 532 realistic prescriptions in which the correct rate lands in the normal band, picking mg/kg/h in place of mcg/kg/min left the rate still inside the normal band 220 times, and picking a flat mg/h did so 403 times. The band reliably catches a thousand-fold mass error and very little else; the read-back and the concentration caught eight of the nine slips tested in every single case.

And then there is the weight, which nothing on this page can check. Type 7 kg instead of 70 and the rate comes out a tenth of what it should be — while the concentration rows are still right, the read-back still reads back exactly the dose that was prescribed, and the rate itself is a perfectly believable number. In the sweep above, that slip left the rate inside the normal band 351 times out of 532 and was the one of the nine that neither check row caught, in any case, ever. No arithmetic can catch it, because the calculation is entirely self-consistent with the wrong weight. The weight has to be read back off the prescription by a person. If an independent check is done before administration — and for a weight-based infusion it should be — the weight is the field to check first, because it is the only one where this page offers no help at all.

Units of heparin and insulin are not milligrams, and the page will not pretend otherwise. A unit is a measure of biological activity defined against a reference standard. There is no general conversion to mass, so if the dose is prescribed in units the bag amount has to be in units too, and vice versa. Mix them and this page returns no answer and says why. The alternative — silently using 1 unit = 1 mg, or any other invented factor — would produce a number indistinguishable from a correct one. The milligram rows are blank for a dose in units for the same reason.

The reverse direction is the handover question. A pump is running at some rate and somebody needs to know what the patient is getting. Put the rate from the pump screen into the box near the bottom and the page gives the dose in mcg/kg/min, mcg/kg/h, mg/h or units/kg/h as appropriate, plus that rate as a percentage of the rate the prescription asks for. When those two disagree, the first thing to suspect is not the rate but the bag: an infusion made up to a different concentration from the one you assumed will give exactly this picture, and correcting the rate rather than the assumption is how it gets worse.

What is not on this page, deliberately. The neonatal glucose infusion rate case — dextrose percentage and mL/h to mg/kg/min of glucose — belongs to the neonatal glucose infusion rate page, which is built for it; this page does not restate it. A loading dose is a separate calculation. Making up the bag from vials is dilution arithmetic: C1V1 = C2V2. Which body weight a prescription should be written against is a prescribing question, covered by the dosing weight page. And a gravity line has no pump and no mL/h to set, so it needs drops per minute instead: the IV drip rate page, which shares this page’s unit vocabulary and rounding conventions so the two can be read together. For what is left in a running bag and when it will finish, the infusion time and remaining volume page.

Frequently asked questions

Why is there a factor of 60 in the mcg/kg/min calculation?

Because the dose is prescribed per minute and the pump is set per hour, and there are sixty minutes in an hour. A dose of 5 mcg/kg/min for a 70 kg patient is 350 micrograms a minute and therefore 21,000 micrograms an hour; the pump needs the per-hour figure. If the prescription had said mcg/kg/h there would be no 60 at all. That is exactly why the two unit options sit next to each other in the dropdown with their full names spelled out: they differ by sixty and by nothing else.

And the factor of 1,000?

That one comes from the bag, not the prescription. Bags and vials are labelled in milligrams while vasoactive doses are prescribed in micrograms, so the concentration has to be expressed in micrograms per mL before the division works. 1.6 mg/mL is 1,600 mcg/mL. For mcg/kg/min from a bag labelled in mg both conversions apply at once, which is why the hand formula is written as “× 60 ÷ 1000” and why that is the step most often fumbled. The page prints the concentration in both mg/mL and mcg/mL so you can see the 1,000 happen.

What exactly should I put in the “volume in the bag” box?

The final volume after the drug has been added, because that is what the pump will push. If 20 mL of drug went into a 250 mL bag with nothing removed, the final volume is 270 mL and the concentration is lower than you would get by assuming 250. Whether the diluent was removed first is a question about how the bag was made up; check rather than assume, because it changes the concentration by 8% in that example. A standard premixed bag states its own final volume on the label.

My pump will only take whole numbers. How much does that matter?

The page tells you for your own numbers: it shows the whole-number rate, the dose that rate actually delivers, and that rate as a percentage of the exact one. At 13.125 mL/h rounding to 13 delivers 99.05% of the prescription, which is nothing. At 1.4 mL/h rounding to 1 delivers 71%, which is a great deal. The general rule follows from it: the lower the rate, the more rounding costs, and below a few mL/h you want a syringe pump that takes decimals rather than a volumetric pump that does not.

Why will it not work out a rate for heparin in units/kg/h from a bag in mg?

Because there is no conversion between units and milligrams. A unit of heparin is an amount of anticoagulant activity measured against an international reference preparation, and the mass that corresponds to it depends on the particular product. The page refuses rather than inventing a factor, because an invented factor would give a number that looked exactly like a correct answer. If the bag is labelled in units, enter units; if the prescription is in units, the bag must be too.

Does the patient’s weight matter for a flat order in mg/h?

Not for the rate. A flat order gives a dose per hour directly, so the mL/h depends only on that dose and the concentration. The page still uses the weight for the equivalent per-kilogram rows, which exist so that a flat order can be compared with a weight-based one — useful when a patient is handed over between units that write the same drug two different ways. If you change the weight with a flat order selected, watch the headline rate not move: that is the page telling you the weight is not in the calculation.

The pump is running at a rate that does not match what this page says. What should I suspect first?

The bag, not the pump. The commonest reason the two disagree is that the infusion hanging was made up to a different concentration from the one assumed — a double-strength bag, a different premixed product, a different local standard concentration. The second commonest is that the prescription was written against a different weight. In both cases the correct response is to find out which, not to change the rate, and in both cases changing the rate first makes it worse. The page gives you the dose the running rate is delivering so you can state the problem precisely to whoever can fix it.

Which mistake is this page least able to help me with?

A wrong weight, and it is worth knowing that before you need it. Every other slip leaves a trace: a wrong dose unit changes the dose read-back, and a wrong bag unit or bag volume changes the concentration rows. A wrong weight changes neither. The rate comes out wrong by whatever factor the weight is wrong by, the concentration is still right because the bag has not changed, and the read-back still shows exactly the dose that was prescribed, because the whole calculation is self-consistent with the weight it was given. Across 532 realistic prescriptions, a weight entered a factor of ten out left the rate inside the normal pump-rate band 351 times and was caught by neither check row in any case at all. So when an infusion is independently checked before administration, the weight is the field to check first: it is the only one where this page offers no help whatsoever.

Does this page tell me what dose to give?

No, and it is built so that it cannot. There is no field for an indication, a diagnosis or a target, and there is no output in milligrams of a dose to give. It takes a prescription that has already been written and works out the rate that delivers it, which is a conversion. Choosing the dose, the drug, the concentration and whether to change a running rate are prescribing decisions.

Related calculators

References

Open Resources for Nursing (Open RN), Nursing Skills, section 5.17 “Multi-Step Calculations”. Open educational resource. Independent worked example used to verify this page: Nipride 50 mg in 250 mL, a 180 lb (81.82 kg) patient, 0.5 mcg/kg/min, answer 12.27 mL/h. This page returns 12.2727 mL/h for the same inputs.
Indian Hills Community College, Associate Degree Nursing dosage-calculation unit (lu03). Second independent source, agreeing with the first: dopamine 800 mg in 250 mL, 70 kg, 3 mcg/kg/min, answer 4 mL/h (this page gives 3.9375, rounding to 4); and propofol at 15 mg/mL, 75 kg, 30 mcg/kg/min, answer 9 mL/h (this page gives exactly 9).
South Eastern Sydney Local Health District, Anticoagulation with Intravenous Heparin Sodium Infusion, SESLHDPR/402 Appendix A. Third independent source, and the one that exercises the units/kg/h path: a premixed 25,000 units in 250 mL bag (100 units/mL) at 18 units/kg/h, with a published starting-rate table running from 7 mL/h at 40 kg to 31 mL/h at 170 kg. This page reproduces both ends and the 720 to 3,060 units/hour column. Cited, not reproduced.
Joint Formulary Committee, British National Formulary, appendix on intravenous additives and the monographs for the individual drugs. The authority for what may be infused at what concentration and in what diluent, none of which this page knows or asks about. Cited, not reproduced.
Verification performed for this page rather than taken from a source: nine ways of mis-entering a prescription were applied across ten weights (2 to 150 kg), ten doses (0.01 to 50 mcg/kg/min) and twelve bag strengths (1 mg in 50 mL to 1.6 g in 250 mL), keeping the 532 combinations in which the correct rate falls in the normal band. The result contradicted this page’s own first draft, which had claimed that every factor-of-sixty and factor-of-a-thousand slip is thrown outside the plausible band: mg/kg/h in place of mcg/kg/min stayed inside it 220 times out of 532, and a flat mg/h did so 403 times. The claim was removed and the table replaced with measured figures. The same sweep established that the dose read-back catches every dose-unit slip and no bag-unit or bag-volume slip, that the concentration rows catch every bag-unit and bag-volume slip and no dose-unit slip, and that a wrong weight is caught by neither — which is why the weight now carries a warning of its own.
Derivation performed for this page rather than taken from a source: reducing every dose unit to one canonical rate (micrograms per hour, or units per hour) through a single multiplier k collapses nine prescription formats into one division. k is 60 for a per-minute order, 1000 for an order in milligrams against a bag read in micrograms, 60000 for mg/kg/min where both apply, and 1 otherwise. For mcg/kg/min against a bag labelled in mg the two combine to 0.06, giving rate = 0.06 × dose × weight × volume / amount_mg — verified against all three sources above and against the internal requirement that seven equivalent ways of writing the same prescription produce the same rate to within floating-point error.

CalcEngines health calculators are for education and for checking arithmetic that has already been decided elsewhere. They are not medical advice, they do not decide what to give, and they do not replace the judgement of a doctor, nurse, midwife or dietitian who knows the person in front of them. Every figure depends on the values you enter and on the assumptions stated on the page — check it against the prescription, the product label and your local policy before acting on it.