Body Surface Area Calculator
Calculate body surface area (BSA) with the Mosteller and Du Bois formulas.
Results update as you type.
About this calculator
A body surface area (BSA) calculator estimates the total external area of your body in square metres from your height and weight. BSA is widely used in medicine to scale drug doses and physiological measurements. This tool uses the simple Mosteller formula and shows the classic Du Bois result for comparison.
Mosteller is a square root: BSA = √(height cm × weight kg ÷ 3600). For a 175 cm, 75 kg person that is √(175 × 75 ÷ 3600) = √3.65 ≈ 1.91 m². Du Bois, which raises height and weight to fractional powers, lands within a few hundredths of the same figure, which is why Mosteller is preferred for quick bedside use. The tool also reports the Haycock, Gehan-George and Boyd equations.
Body surface area matters most in dosing: chemotherapy and some other drugs are prescribed in milligrams per square metre, and measures like cardiac index are normalised to BSA because surface area tracks metabolic rate better than weight alone. Enter height and weight in metric or imperial and the tool converts internally. Dosing and clinical decisions belong to a clinician; this calculator is for reference only.
Frequently asked questions
What is the Mosteller BSA formula?
BSA (m²) = square root of (height in cm × weight in kg ÷ 3600). It is the most common formula because it is easy to compute yet closely matches more complex equations.
Why is body surface area used in medicine?
Many drug doses — especially chemotherapy — and measures like cardiac index are scaled to BSA rather than weight, because surface area tracks metabolic rate more closely than body mass alone.
What is a normal body surface area?
Average adults fall around 1.7 m² for women and 1.9 m² for men. A 175 cm, 75 kg person is about 1.91 m² by the Mosteller formula.
Why does this tool show several BSA formulas?
Mosteller, Du Bois, Haycock, Gehan-George and Boyd were each derived from different measured samples, so their numbers differ slightly. They agree within a few percent for typical adults, and Mosteller is favoured for being both simple and accurate.
How is BSA used to calculate a drug dose?
Doses in milligrams per square metre are multiplied by your BSA — so a 100 mg/m² drug at a BSA of 1.9 m² gives 190 mg. Actual dosing is set by a clinician; this tool only estimates the surface area.
Do I enter height in centimetres or inches?
Either — pick the matching units and the tool converts to centimetres and kilograms, which the formulas require. Mosteller itself is the square root of height in cm times weight in kg divided by 3,600.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/body-surface-area/curl
curl "https://calculator.free/api/v1/body-surface-area/?units=metric&height=175&weight=75"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/body-surface-area/?" + new URLSearchParams({
"units": "metric",
"height": "175",
"weight": "75"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.