Ideal Body Weight (IBW) Calculator
An ideal body weight calculator comparing all four formulas plus adjusted body weight, and why they disagree by up to 12 kg at tall heights.
Formula Breakdown Comparison
What Ideal Body Weight (IBW) Calculator Does
Clinical references tell a different story. MDCalc, the Merck Manual and ClinCalc all present ideal body weight as a clinical parameter: for drug dosing, for estimating renal function, for setting a ventilator. Merck files it under mechanical ventilation. That is what these equations are actually used for.
They were never a health target. A review of their origins traced all of them back to mid-century insurance height-weight tables, which recorded what people of a given height weighed and how that correlated with mortality. The word "ideal" attached itself along the way. Devine's version, the one most calculators use, entered clinical practice in 1974 because the pharmacokinetics of certain drugs happened to correlate with it.
That history explains something you can see in the numbers. The four formulas agree closely around average height (about 1.4 kg apart for a woman of 5ft 8in) and then fan out as you move away from the middle, reaching 12.4 kg of disagreement for a man of 6ft 4in. They agree in the middle because they were fitted to the same tables rather than because four independent lines of evidence converged.
So use this page for what it is good for: comparing the formulas, working out adjusted body weight, or setting a lung-protective tidal volume. If the question is what you should weigh, the honest answer is a range rather than a number, and the healthy BMI band for someone 5ft 10in spans about 20 kilograms.
How to Use Ideal Body Weight (IBW) Calculator
- Select your biological gender
- Choose Metric (centimeters) or Imperial (feet & inches)
- Input your height
- View your averaged ideal body weight, healthy recommended range, and formula comparisons
Formula Used by Ideal Body Weight (IBW) Calculator
The four ideal body weight equations
IBW = base weight + increment × (inches over 5 feet)
- Devine (1974)
- Men 50.0 kg + 2.3 kg/in · Women 45.5 kg + 2.3 kg/in
- Robinson (1983)
- Men 52.0 kg + 1.9 kg/in · Women 49.0 kg + 1.7 kg/in
- Miller (1983)
- Men 56.2 kg + 1.41 kg/in · Women 53.1 kg + 1.36 kg/in
- Hamwi (1964)
- Men 48.0 kg + 2.7 kg/in · Women 45.5 kg + 2.2 kg/in
Worked example
A man of 5ft 10in, 10 inches over 5 feet
- Devine: 50.0 + (2.3 × 10) = 73.0 kg
- Robinson: 52.0 + (1.9 × 10) = 71.0 kg
- Miller: 56.2 + (1.41 × 10) = 70.3 kg
- Hamwi: 48.0 + (2.7 × 10) = 75.0 kg
Result: 70.3 to 75.0 kg; all four sit at a BMI between 22.2 and 23.7
Adjusted body weight — for drugs that distribute into fat
ABW = IBW + 0.4 × (actual weight − IBW)
- 0.4
- The share of excess weight treated as contributing to drug distribution
Worked example
A man of 5ft 10in weighing 110 kg (Devine IBW 73.0 kg)
- Excess over IBW: 110 − 73.0 = 37.0 kg
- 40% of that: 0.4 × 37.0 = 14.8 kg
- 73.0 + 14.8
Result: 87.8 kg, which is 22.2 kg below his actual weight and 14.8 kg above his ideal weight
Where the four formulas agree, and where they do not
Ideal body weight in kilograms for men. Agreement is tightest near average height because all four descend from the same height-weight tables; they diverge as each extrapolates on its own slope.
| Height | Devine | Robinson | Miller | Hamwi | Spread |
|---|---|---|---|---|---|
| 5ft 0in | 50.0 | 52.0 | 56.2 | 48.0 | 8.2 kg |
| 5ft 4in | 59.2 | 59.6 | 61.8 | 58.8 | 3.0 kg |
| 5ft 8in | 68.4 | 67.2 | 67.5 | 69.6 | 2.4 kg |
| 6ft 0in | 77.6 | 74.8 | 73.1 | 80.4 | 7.3 kg |
| 6ft 4in | 86.8 | 82.4 | 78.8 | 91.2 | 12.4 kg |
The same comparison for women
Closest agreement lands at 5ft 8in, where the four differ by only 1.4 kg.
| Height | Devine | Robinson | Miller | Hamwi | Spread |
|---|---|---|---|---|---|
| 5ft 0in | 45.5 | 49.0 | 53.1 | 45.5 | 7.6 kg |
| 5ft 4in | 54.7 | 55.8 | 58.5 | 54.3 | 4.2 kg |
| 5ft 8in | 63.9 | 62.6 | 64.0 | 63.1 | 1.4 kg |
| 6ft 0in | 73.1 | 69.4 | 69.4 | 71.9 | 3.7 kg |
| 6ft 4in | 82.3 | 76.2 | 74.9 | 80.7 | 7.4 kg |
Lung-protective tidal volume from ideal body weight
Ventilator volumes are set against ideal body weight because lung size tracks height rather than weight. Using Devine at 6–8 ml per kg.
| Height | Male IBW | Male tidal volume | Female IBW | Female tidal volume |
|---|---|---|---|---|
| 5ft 2in | 54.6 kg | 328–437 ml | 50.1 kg | 301–401 ml |
| 5ft 6in | 63.8 kg | 383–510 ml | 59.3 kg | 356–474 ml |
| 5ft 10in | 73.0 kg | 438–584 ml | 68.5 kg | 411–548 ml |
| 6ft 2in | 82.2 kg | 493–658 ml | 77.7 kg | 466–622 ml |
How to Read Your Result
A range, not a number
For someone 5ft 10in, a BMI between 18.5 and 24.9 corresponds to roughly 58.5 kg to 78.7 kg. Every formula on this page returns a value inside that band, which tells you what they are: one plausible point in a twenty-kilogram window. Someone at 62 kg and someone at 77 kg are both within the healthy range at that height, and no equation can say which of them is at their own best weight.
Why weight is set against height for ventilators
Lungs scale with height and with frame rather than with body fat. A person who gains 40 kg has the same lung capacity they had before. Lung-protective ventilation therefore sets tidal volume against ideal body weight, typically 6 to 8 ml per kilogram, about 438 to 584 ml for a 5ft 10in man whatever he actually weighs. Setting that volume from actual weight in a heavier patient would over-distend the lungs, which is the harm the approach exists to prevent.
Neither ideal nor actual weight doses every drug correctly
Water-soluble drugs distribute mainly through lean tissue, so dosing on actual weight in someone carrying substantial fat overshoots. Fat-soluble drugs distribute into adipose tissue, so dosing on ideal weight undershoots. Adjusted body weight (ideal plus 40% of the excess) is the compromise used for drugs that fall between. This is a prescriber's decision and depends entirely on the specific drug.
The gap between men and women is a constant, which is a clue
In the Devine equation men and women use the same 2.3 kg per inch, so the difference between them is a flat 4.5 kg at every height, the same gap at 5ft 0in as at 6ft 4in. Real differences in body composition between the sexes do not behave like a constant offset. It is a reminder that these are simple linear fits to old tables rather than descriptions of physiology.
Where the formulas are least trustworthy
Below 5 feet the equations return their base weight with nothing subtracted, so they are not meaningful for shorter adults, and some clinical practice subtracts a per-inch amount instead. At the tall end the four answers spread over 12 kg, because each is extrapolating past the height range its source tables covered. The middle of the height distribution is exactly where they were fitted and exactly where they agree.
Limitations & Accuracy Notes
- These equations descend from mid-century insurance height-weight tables. They were not derived from studies of health outcomes, and their agreement with one another reflects a shared source rather than independent validation.
- Height is the only input. Frame size, muscularity, age, sex beyond a flat offset, and ethnicity are all absent, so the same number is returned for a heavily muscled person and a sedentary one of identical height.
- The formulas disagree by up to 12.4 kg at tall heights and 8.2 kg at short ones. Any single figure quoted to one decimal place carries far more apparent precision than the underlying method supports.
- Ideal body weight is not a weight-loss target and was never intended as one. Using it that way inverts its purpose, and for anyone with a history of disordered eating a single prescribed "ideal" number can be actively harmful.
- The clinical applications shown here (adjusted body weight, tidal volume) are included to explain what the measure is for rather than as dosing or ventilator guidance. Those are decisions for the treating clinician.
Frequently Asked Questions
What is ideal body weight actually for?
Mostly drug dosing and ventilator settings rather than personal weight goals. A review of where these equations came from found they descend from mid-century insurance height-weight tables, and that Devine's version entered practice because the pharmacokinetics of certain drugs correlated with it. That is why clinical references such as MDCalc, the Merck Manual and ClinCalc present it alongside drug dosing and mechanical ventilation.
Why do the four formulas give different answers?
Because they are different regressions of the same underlying height-weight tables. Near average height they agree closely, about 1.4 kg apart for a 5ft 8in woman. They diverge as you move away from the middle, because each extrapolates on its own slope: for a 6ft 4in man the four answers span 12.4 kg. The agreement in the middle reflects a shared source rather than independent confirmation.
Is there a single ideal weight for my height?
No, and the precision of a single number is misleading. For someone 5ft 10in, the healthy BMI band of 18.5 to 24.9 spans roughly 58.5 kg to 78.7 kg, a 20 kg window. Every formula on this page returns a number somewhere inside that window, so what they really produce is one plausible point in a wide healthy range.
What is adjusted body weight and when is it used?
Adjusted body weight is ideal body weight plus 40% of the excess over it: ABW = IBW + 0.4 × (actual − IBW). It exists because some drugs distribute partly into fat tissue, so neither ideal nor actual weight dose correctly. For a 5ft 10in man weighing 110 kg, IBW is 73 kg and adjusted body weight is 87.8 kg, which is 22 kg below his actual weight.
Why do ventilator settings use ideal body weight?
Because lung size tracks height rather than weight. Someone who gains 40 kg does not gain lung capacity, so lung-protective ventilation sets tidal volume against ideal body weight, commonly 6 to 8 ml per kg. For a 5ft 10in man that is roughly 438 to 584 ml regardless of what he actually weighs. Dosing that volume on actual weight would over-inflate the lungs.
Where do these formulas come from?
Devine, Robinson, Miller and Hamwi were developed mainly for calculating drug dosages rather than for setting health targets. That origin is the single most important thing to know about them: they were never intended as a goal weight for an individual.
Why do the formulas disagree?
Because each was fitted to a different population with different assumptions, and none accounts for body composition or frame size. A spread of several kilograms between them is normal and is a useful indication of how imprecise the whole concept is.
Should I aim for my "ideal" weight?
Not as a target in itself. Two people of identical height and weight can have completely different body composition and health. Body fat percentage, waist measurement, fitness and blood markers all say more about health than a number derived from height alone.
Do the formulas work for very short or very tall people?
Poorly. Most are linear extrapolations from a baseline height and become increasingly unrealistic at the extremes, which is one reason clinical use has moved toward adjusted or lean body weight for dosing.
Do they account for muscle?
Not at all. An athlete will frequently exceed every formula's output while carrying low body fat, which illustrates the limitation rather than indicating a problem.
Is this medical advice?
No. It applies published formulas to your height. Weight goals belong in a conversation with a clinician who knows your history.
References & Further Reading
- Pai MP, Paloucek FP — The origin of the "ideal" body weight equations — Ann Pharmacother 2000;34(9):1066-9, which traces all four equations to insurance height-weight tables and explains how Devine's entered practice through drug pharmacokinetics
- NHLBI — Calculate your BMI — The 18.5–24.9 healthy BMI band used to derive the healthy weight range quoted above
- NHLBI — Overweight and obesity — Background on how weight categories relate to health risk, and why a range is more meaningful than a single target