⚖️ 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
Look at who Google ranks for this term and the picture changes. MDCalc, Merck and ClinCalc all appear on page one, and all three 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, not 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, not 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 — 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, not 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, not 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, not as dosing or ventilator guidance. Those are decisions for the treating clinician.
Frequently Asked Questions
What is ideal body weight actually for?
Why do the four formulas give different answers?
Is there a single ideal weight for my height?
What is adjusted body weight and when is it used?
Why do ventilator settings use ideal body weight?
Where do these formulas come from?
Why do the formulas disagree?
Should I aim for my "ideal" weight?
Do the formulas work for very short or very tall people?
Do they account for muscle?
Is this medical advice?
References & Further Reading
- Pai MP, Paloucek FP — The origin of the "ideal" body weight equations — Ann Pharmacother 2000;34(9):1066-9 — 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