What it does
Clinical teaching uses a handful of body size measures again and again: body mass index (BMI), body surface area (BSA), ideal body weight (IBW), adjusted body weight (ABW) and lean body weight (LBW). Each has more than one published formula, and the formulas give slightly different answers. This page works them all out side by side from one height and weight, shows each formula next to its result, and places the person on a weight-for-height chart with the WHO BMI lines. It is for study and teaching, not medical advice.
How to use it
- Choose Metric (cm and kg) or US (feet, inches and pounds). Switching carries your numbers across.
- Choose the sex. BMI and BSA do not use it, but the ideal and lean weight formulas were fitted separately for men and women.
- Type the height and weight. Results update as you type.
- The adjusted-weight factor is the share of the weight above ideal that counts towards the adjusted weight. 0.4 is the value most texts use; some use 0.3 or 0.5.
- Download the results as an image, PDF or Word file.
The formulas
- BMI = weight (kg) ÷ height (m)². The WHO adult classes (WHO 2000) are under 18.5 underweight (split at 16 and 17 into severe, moderate and mild thinness), 18.5 to under 25 normal range, 25 to under 30 pre-obese, and 30, 35 and 40 for obese classes I, II and III. They are for adults only; children use BMI-for-age charts, and some countries use lower cut points for some groups.
- BSA (m²): Mosteller (1987) √(height cm × weight kg ÷ 3600); DuBois and DuBois (1916) 0.007184 × W^0.425 × H^0.725; Haycock (1978) 0.024265 × W^0.5378 × H^0.3964; Gehan and George (1970) 0.0235 × W^0.51456 × H^0.42246.
- IBW: Devine (1974) 50 kg for men or 45.5 kg for women plus 2.3 kg per inch over 5 feet; Robinson (1983) 52 + 1.9 (men) or 49 + 1.7 (women); Miller (1983) 56.2 + 1.41 (men) or 53.1 + 1.36 (women). Below 5 feet they are extrapolated, and the page warns you.
- ABW = Devine IBW + factor × (actual weight − IBW).
- LBW (Janmahasatian 2005) = 9270 × W ÷ (6680 + 216 × BMI) for men, or 9270 × W ÷ (8780 + 244 × BMI) for women.
Worked example
The page opens with a man 180 cm tall weighing 100 kg. His BMI is 30.9 kg/m², WHO class Obese class I. BSA is 2.24 m² (Mosteller), 2.20 (DuBois), 2.26 (Haycock) and 2.25 (Gehan and George). Ideal body weight is 75.0 kg (Devine), 72.6 (Robinson) and 71.5 (Miller). His actual weight is 133 % of the Devine IBW, so the adjusted weight, 75.0 + 0.4 × (100 − 75.0), is 85.0 kg, and the lean body weight is 69.5 kg.
Tips
- The four BSA formulas agree within a few per cent for average adults and drift apart for very large or very small people. That spread is a useful reminder that BSA is an estimate.
- Ideal body weight depends only on height and sex, never on the actual weight.
- These numbers feed other formulas, such as the Cockcroft-Gault creatinine clearance. They are not instructions for treatment.
FAQ
Which BSA formula is right? None is exact. Mosteller is the simplest and very widely taught; DuBois is the oldest; Haycock was fitted on children as well as adults.
Why does my BMI class differ from another chart? Some countries and groups use different cut points, and BMI-for-age is used for children. Check the official source for your setting.
Is anything sent or saved? No. Everything is worked out in your browser and nothing about you is stored.
Where the numbers come from
- BMI classes: World Health Organization, Obesity: preventing and managing the global epidemic, WHO Technical Report Series 894 (2000), adult cut points 16, 17, 18.5, 25, 30, 35 and 40 kg/m² (checked 2026-11-09; check the official source).
- Body surface area: R. D. Mosteller, N Engl J Med 317:1098 (1987); D. DuBois and E. F. DuBois, Arch Intern Med 17:863 (1916); G. B. Haycock, G. J. Schwartz and D. H. Wisotsky, J Pediatr 93:62 (1978); E. A. Gehan and S. L. George, Cancer Chemother Rep 54:225 (1970). Formulas only.
- Ideal body weight: B. J. Devine, Drug Intell Clin Pharm 8:650 (1974); J. D. Robinson et al., Am J Hosp Pharm 40:1016 (1983); D. R. Miller et al., Am J Hosp Pharm 40:1622 (1983). Adjusted body weight with the 0.4 factor as used in clinical pharmacokinetics texts (e.g. L. A. Bauer, Applied Clinical Pharmacokinetics). Lean body weight: S. Janmahasatian et al., Clin Pharmacokinet 44:1051 (2005). Formulas only.
- Checked in the tests against an independent Python implementation of the same formulas on ten adults, and by hand (6 ft man: Devine 77.6 kg).
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.