Body Surface Area (BSA) Calculator
Calculate body surface area in m² from height and weight with the Mosteller, Du Bois, Haycock, Gehan & George and Boyd formulas side by side.
Body surface area (BSA) estimates the area of the body in square meters from height and weight. It is used in some clinical indexing and dosing protocols. This page compares five published equations; it does not select a drug dose or determine which formula a treatment protocol requires.
How to use this tool
- Choose centimetres and kilograms, or inches and pounds.
- Enter height and weight.
- Read the Mosteller result at the top, and compare it with Du Bois, Haycock, Gehan & George and Boyd in the results and table.
Formula
Mosteller: BSA (m²) = √(height in cm × weight in kg ÷ 3600)
Du Bois: 0.007184 × W^0.425 × H^0.725. Haycock: 0.024265 × W^0.5378 × H^0.3964. Gehan & George: 0.0235 × W^0.51456 × H^0.42246. Boyd: 0.0003207 × H^0.3 × G^(0.7285 − 0.0188 × log₁₀G), with G the weight in grams. H is height in cm and W weight in kg; US entries are converted first (1 in = 2.54 cm, 1 lb = 0.45359237 kg). 1 m² = 10.764 ft².
Example
For 180 cm and 80 kg, Mosteller gives √(180 × 80 ÷ 3600) = √4 = 2.00 m² (21.53 ft²). Du Bois gives 1.996 m², Haycock 2.007, Gehan & George 2.009 and Boyd 2.007, so for an average adult build the five formulas agree to within about 0.7%.
Frequently asked questions
Which BSA formula should I use?
Use the equation specified by the clinical or research protocol. Mosteller is simple to calculate, while Haycock was developed with infants, children and adults. The formulas are alternatives fitted to different samples, not interchangeable rules for every clinical purpose.
What is a normal body surface area?
BSA varies with body size; there is no universal healthy interval. The value 1.73 m² is a reference used for reporting indexed kidney function, not a target body size or a diagnostic threshold.
Why do the formulas give different answers?
Each one was fitted to a different group of people measured in a different way. They agree well near average height and weight and drift apart at the extremes, for example in severe obesity or very small children.
Sources
- Mosteller RD. Simplified calculation of body-surface area. N Engl J Med, 1987
- Du Bois D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med, 1916
- SCMR reporting guidelines, Table 1 — all five BSA equations
This tool gives an estimate for general information only. It is not financial, tax, legal or medical advice — check with a qualified professional before you rely on the result.
Last updated: 2026-10-30