Clinical calculator · August 2026
Ideal body weight calculator: IBW, adjusted body weight and dosing weight
Enter height and sex for ideal body weight by all four published equations at once. Add the current weight and it also returns adjusted body weight and percent of ideal.
Devine, Robinson, Miller and Hamwi disagree by several kilograms in the same patient. The section below explains why, and which one your protocol probably already means.
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Devine, Robinson, Miller, Hamwi
Calculate ideal and adjusted body weight
Ideal body weight (Devine)
kg ( lb)
Actual weight is percent of ideal. Most protocols reach for adjusted weight in this range. Below roughly 120 percent the adjusted and actual figures converge.
Enter sex and height to see ideal body weight by all four equations. Add the current weight for adjusted body weight and percent of ideal.
Weights only. No dose is recommended. Verify before prescribing.
The short answer
How do you calculate ideal body weight?
Ideal body weight by the Devine equation is 50 kg for men or 45.5 kg for women, plus 2.3 kg for every inch of height above 60 inches. Height is the only input, so the answer does not move when the patient's weight does. Adjusted body weight is that figure plus 0.4 of the gap between actual and ideal weight, and it is what most protocols use once a patient sits well above their ideal weight. Devine is the US pharmacy default; Robinson, Miller and Hamwi exist and give different answers.
Every equation and citation on this page was checked at its source in August 2026. Last updated August 2026.
Four equations, four different answers
The ideal body weight formulas compared
Each one was built for a specific drug or diet problem, and none of them was built to describe a healthy weight.
| Equation | Male | Female | Originally built for |
|---|---|---|---|
| Devine 1974 | 50 kg + 2.3 kg per inch over 60 in | 45.5 kg + 2.3 kg per inch over 60 in | Gentamicin dosing in obese patients |
| Robinson 1983 | 52 kg + 1.9 kg per inch over 60 in | 49 kg + 1.7 kg per inch over 60 in | Refining weight for drug dosage calculations |
| Miller 1983 | 56.2 kg + 1.41 kg per inch over 60 in | 53.1 kg + 1.36 kg per inch over 60 in | Digoxin dosing work |
| Hamwi 1964 | 106 lb + 6 lb per inch over 60 in | 100 lb + 5 lb per inch over 60 in | Rapid diet and insulin estimates in diabetes |
Devine
1974The US pharmacy default, and the equation almost every hospital protocol means when it writes IBW.
Robinson
1983Published in the American Journal of Hospital Pharmacy. Runs lower than Devine at tall heights.
Miller
1983Highest base weight, smallest per-inch increment, so it reads high in short adults and low in tall ones.
Hamwi
1964The oldest of the four and the one still taught in dietetics. Published in pounds.
The spread is not academic. For a man of 70 inches, Devine returns 73 kg, Robinson 71 kg and Miller 70.3 kg. For a woman of 62 inches the gap runs the other way: Devine 50.1 kg, Robinson 52.4 kg, Miller 55.8 kg. Miller carries the highest base weight and the smallest per-inch increment, so it reads high in short adults and low in tall ones, and it crosses the other two somewhere in the middle of the adult height range.
Which is right? None of them, in the sense the question implies. The historical review by Pai and Paloucek traces all four back to mid-century insurance height and weight tables rather than to any outcome data, and it is the reason the word ideal in this context should be read as a dosing convention. Devine came out of gentamicin work, Miller out of digoxin work, Hamwi out of diabetes diet planning. They were shortcuts that worked well enough for the drug in front of their authors, and they stuck.
The practical answer is to pick one and write it down. A US hospital protocol that says IBW without qualifying it almost always means Devine, which is why that is the figure this calculator reports first and the figure it uses to derive adjusted weight.
The choice that moves the number
Actual, ideal or adjusted body weight?
Three defensible answers for the same patient, and the drug decides which one applies.
Actual body weight (ABW)
The measured weight on the scale
What the patient weighs today. Most mg/kg labeling is written against it, and it is the correct input whenever a patient sits at or below their ideal weight. It is also the number that stops behaving as a dosing proxy once adipose tissue is a large share of it, because most drugs do not distribute into fat the way they distribute into lean mass.
Ideal body weight (IBW)
A height-derived estimate of lean mass
Not a health target and never was. It is a height-based stand-in for lean body mass that lets a dose track the compartment a drug actually reaches. Because it ignores the scale entirely, two patients of the same height get the same IBW at 60 kg and at 160 kg, which is the point and also the limitation.
Adjusted body weight (AdjBW)
Obesity, where neither ABW nor IBW fits
Ideal body weight plus a fraction of the gap between actual and ideal, conventionally 0.4. It concedes that adipose tissue is not pharmacokinetically inert without pretending it behaves like lean mass. Some drug-specific protocols use 0.3 or 0.5 instead, so the factor is a local decision rather than a universal constant.
Adjusted body weight (kg)
IBW + 0.4 × (actual body weight − IBW)
Some drug-specific protocols substitute 0.3 or 0.5 for the correction factor.
The reason adjusted body weight exists at all is that neither of the other two options survives contact with obesity. Actual weight assumes a drug distributes into adipose tissue the way it distributes into lean mass, which for most hydrophilic drugs it does not. Ideal weight assumes adipose tissue is pharmacokinetically invisible, which is also false, and errs toward under-treatment. The 0.4 factor is a compromise that has held up in practice rather than a constant derived from physiology, and you will find 0.3 and 0.5 in specific protocols without either being wrong.
Where this bites hardest is renal dosing, because the weight is an input to Cockcroft-Gault before it is an input to anything else. Switching a 118 kg patient from actual to ideal weight can move the estimate across a labeled threshold and change the recommended interval, which is why the creatinine clearance calculator makes the weight basis an explicit selection rather than a hidden default. The same choice propagates into renal dose adjustment and into the agents on the list of drugs to avoid in renal failure, where the margin is narrow enough that a weight convention decides the answer.
For vancomycin the profession largely stopped arguing about weight conventions and moved to measured concentrations, which is a different and better answer to the same problem. The vancomycin AUC calculator runs that two-level arithmetic once levels are back.
The questions behind the searches
What clinicians actually want to know about IBW
Is ideal body weight the same as a healthy weight?
No, and the confusion is costly in both directions. The four common equations were built for drug dosing and diet estimates, not for health outcomes, and they were derived from insurance height and weight tables rather than from mortality or morbidity data. Nothing about a patient's ideal body weight tells you whether their current weight is healthy for them.
That distinction matters clinically because a patient who sees an IBW figure in their chart reasonably reads it as a target. It is not one. It is a stand-in for lean mass that lets a milligram-per-kilogram dose track the compartment a drug actually reaches, which is a question about pharmacokinetics rather than about the patient's health.
Why use adjusted body weight instead of actual body weight?
Because in obesity the scale weight stops predicting the volume a drug distributes into. Hydrophilic drugs stay largely in lean tissue and extracellular water, so dosing them on a weight that is substantially adipose gives a larger dose than the patient's pharmacokinetics call for. Lipophilic drugs behave differently, which is exactly why the answer is drug-specific rather than universal.
Adjusted body weight adds back a defined fraction of the excess, conventionally 40 percent, so it lands between the two failure modes. Just as important, it is reproducible: two pharmacists who both follow the protocol get the same number, which is not true of clinical judgment applied fresh each time.
When to calculate adjusted body weight?
When actual body weight sits meaningfully above ideal body weight and the drug is dosed on a lean-mass proxy. Many institutional protocols set the trigger at actual weight exceeding ideal weight by 20 to 30 percent, which is why this calculator shows percent of ideal alongside the adjusted figure. Below that threshold the adjusted and actual weights converge and the extra step changes nothing.
The reverse case is worth naming too. A patient below their ideal body weight should generally be dosed on actual weight, because using a height-derived ideal figure would give a frail or cachectic patient a dose calculated for a heavier person. Ideal body weight is a ceiling in that situation, not a substitute.
How do you calculate ideal body weight for an amputation?
Estimate the proportion of total body weight the missing segment represented, then reduce the height-derived ideal weight by that proportion before using it for anything else. The height itself also needs care, since a standing height is unavailable and an estimate from arm span or knee height carries its own error into every equation on this page.
The published segment proportions clinicians work from trace back to Osterkamp in the Journal of the American Dietetic Association in 1995. Reproductions of that table on the open web disagree at the first decimal place, sometimes by a full percentage point on a whole limb, so use the table written into your own institutional protocol rather than a figure found online. This is one of the few places where sourcing the number locally genuinely matters more than sourcing it correctly.
What is predicted body weight for ventilator settings?
Predicted body weight is the same height-based arithmetic as Devine ideal body weight, applied to a different question. Low tidal volume ventilation sets tidal volume in millilitres per kilogram of predicted rather than actual weight, on the reasoning that lung volume scales with height and not with adipose tissue.
The practical consequence is that one height error propagates into two unrelated decisions at once, the ventilator setting and the drug dose. If the chart height came from the patient rather than a measurement, both are softer than they look.
Getting it right in practice
Four steps to using a body weight estimate for dosing
The arithmetic is trivial. The failure modes are procedural.
Measure the height, do not ask for it
Every equation here is driven entirely by height, so a self-reported figure carries straight through to the answer. Adults over-report height by a small but consistent margin, and in a short patient one inch moves Devine IBW by 2.3 kg. If the chart height came from the patient rather than a stadiometer, treat the result as softer than it looks.
Decide the basis before you see the number
Pick actual, ideal or adjusted from the drug and the protocol, not from which answer looks more comfortable. Choosing the basis after seeing three candidate weights is how the same patient ends up dosed differently on two consecutive shifts.
Use one equation across the institution
Devine, Robinson, Miller and Hamwi disagree by several kilograms in the same patient, and none of them is right in a way the others are wrong. What matters is that the pharmacist recalculating at 3am reproduces the number in the chart. Write the chosen equation into the protocol and stop relitigating it.
Carry it into the clearance estimate, then verify
For a renally cleared drug the weight is an input to Cockcroft-Gault before it is an input to anything else, so the basis you pick here changes the clearance band downstream. Check the result against official labeling and your institutional protocol before it touches an order.
Where the number goes next
A dosing weight is one line of a prescribing check
Getting the weight basis right and then missing that the same patient is on an interacting drug produces a carefully calculated dose of the wrong medication. Weight, renal function, interactions and contraindications are one decision at the bedside even though most tools split them into four lookups.
Prescriber.io puts them in a single card: the interaction, the contraindication, the renal and hepatic dosing consideration, and a cited source for each. The licensed clinician reviews it, verifies against official labeling, and signs. It is decision support, not autonomous prescribing, and it does not replace the arithmetic above.
Teams comparing what the established references cover here can start with the drug reference app comparison, and pharmacy buyers pricing a multi-seat contract should read the institutional license guide.
Press Run check to see the interaction, contraindication, and dosing decision-support card for this scenario.
This on-page demo only ships with five illustrative scenarios and never invents clinical output, so it will not fake a card for this pair.
The full Prescriber.io desk checks any regimen against interactions, contraindications, and renal or hepatic dosing, with cited sources for you to verify.
Interaction
Contraindication / allergy check
Dosing guidance (renal / hepatic)
Guideline-based alternatives
Illustrative sample · not real clinical advice · you verify and decide
Clinician-in-the-loopDecision support for licensed clinicians. Prescriber.io does not diagnose or prescribe and is not a substitute for professional clinical judgment.
Where the equations come from
The primary sources behind this page
Pai and Paloucek, 2000
Pai MP, Paloucek FP. "The origin of the ideal body weight equations." The Annals of Pharmacotherapy, 2000, volume 34, pages 1066 to 1069. The historical review that traces where each equation came from and why the word ideal in this context describes a dosing convention rather than a health target.
Devine, 1974
B.J. Devine proposed the 50 kg and 45.5 kg base weights with a 2.3 kg per inch increment in the context of gentamicin dosing in obese patients. The equation has been cited in more than two hundred articles since, which is how a single aminoglycoside dosing suggestion became the default definition of ideal body weight in US pharmacy.
Robinson and Miller, both 1983
Both refinements appeared in the American Journal of Hospital Pharmacy in the same year, Robinson for drug dosage generally and Miller in digoxin work, and both drew on Metropolitan Life insurance height and weight tables. Miller used the 1983 revision of those tables where Robinson used the earlier edition, which is most of why the two disagree.
Straight answers
Questions clinicians actually search about body weight equations
How do you calculate ideal body weight?
Use the Devine equation: 50 kg for men or 45.5 kg for women, plus 2.3 kg for every inch of height over 60 inches. A 70 inch man comes out at 73 kg, a 64 inch woman at 54.7 kg. Height is the only patient input, so the number does not change when the patient gains or loses weight.
What is adjusted body weight?
Adjusted body weight is ideal body weight plus 0.4 times the difference between actual and ideal body weight. It is used when a patient is well above their ideal weight and neither the scale weight nor the height-derived ideal weight is a good proxy for the compartment a drug distributes into. The 0.4 correction factor is the usual convention, not a law.
Why use adjusted body weight?
Because in obesity actual body weight tends to overshoot and ideal body weight tends to undershoot. Adipose tissue is not pharmacokinetically inert, so ignoring it entirely under-treats, while treating it as though it were lean mass over-treats. Adjusted body weight splits the difference in a way that is reproducible between clinicians, which matters as much as the estimate itself.
When to calculate adjusted body weight?
When actual body weight sits meaningfully above ideal body weight and the drug in front of you is dosed on a lean-mass proxy. Many protocols use a trigger such as actual weight exceeding ideal weight by 20 to 30 percent. Below that threshold the adjusted and actual figures converge and the extra arithmetic buys nothing.
What is the difference between ideal body weight and adjusted body weight?
Ideal body weight is calculated from height alone and ignores what the patient actually weighs. Adjusted body weight starts from that ideal figure and adds back a fraction, conventionally 40 percent, of the excess over it. In a patient at their ideal weight the two are identical; in a patient at twice their ideal weight they differ substantially.
Which ideal body weight formula is used in pharmacy?
Devine, in almost all US hospital pharmacy practice. It is the equation embedded in renal dosing protocols, aminoglycoside nomograms and most electronic health record calculators. Robinson and Miller appear in the literature and Hamwi survives in dietetics, but a US protocol that says IBW without qualifying it almost always means Devine.
What is the Devine formula?
A height-based estimate of lean body weight published by B.J. Devine in 1974: 50 kg for men, 45.5 kg for women, plus 2.3 kg per inch above 60 inches. Devine proposed it to improve gentamicin dosing in obese patients, which is worth remembering, because it was designed as a dosing convenience rather than a statement about healthy weight.
Is ideal body weight the same as a healthy weight?
No. The four common equations were built for drug dosing and diet estimates, not for health outcomes, and they were derived from mid-century insurance height and weight tables rather than from mortality or morbidity data. Devine came from gentamicin work, Miller from digoxin work, Hamwi from diabetes diet planning. None of them was validated as a health target.
How do you calculate ideal body weight for an amputation?
Estimate the proportion of body weight the missing segment represented and reduce the height-derived ideal weight by that proportion before using it. The published segment proportions clinicians work from trace back to Osterkamp, Journal of the American Dietetic Association, 1995, and the exact figures differ slightly between reproductions, so use the table in your own institutional protocol rather than a number found online.
What is predicted body weight for ventilator settings?
Predicted body weight uses the same height-based arithmetic as Devine ideal body weight and is the basis for low tidal volume ventilation, where tidal volume is set in mL per kg of predicted rather than actual weight. It is a different clinical question from drug dosing but the same equation, which is why a single height error propagates into both.
Go deeper
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Creatinine clearance calculator
Cockcroft-Gault, with the weight basis from this page as an input.
CalculatorVancomycin AUC calculator
Where measured levels replace the weight convention entirely.
ToolRenal dosing calculator
Adjustments surfaced against kidney function, with the source cited.
ToolAntibiotic dosing calculator
The class where the weight convention is argued about most.
GuideBest vancomycin dosing software
Free two-level equations against paid Bayesian platforms.
GuideBest drug reference app
What each reference covers, what it costs, who it suits.
The dosing weight belongs in the same check as the interaction.
Prescriber.io checks interactions, flags contraindications, surfaces renal and hepatic dosing and suggests guideline-based alternatives, with cited sources. You review, verify, and sign.
Decision-support for licensed clinicians. The calculator on this page performs published arithmetic and reports weights only. It does not suggest a dose, an interval or a regimen. Prescriber.io does not diagnose or prescribe autonomously and is not a substitute for professional clinical judgment. Always verify against official sources.