By Zencalcy Editorial TeamLast reviewed About us
Body surface area (BSA) estimates the total external surface of the body in square metres. It is used in clinical settings for dosing some drugs, indexing cardiac output, and normalising physiological measurements. Different formulas give slightly different results, so the same formula should be used consistently.
Calculate body surface area with four published formulas.
Du Bois: 0.007184 × height^0.725 × weight^0.425 Mosteller: √(height × weight ÷ 3600) Haycock: 0.024265 × height^0.3964 × weight^0.5378 Boyd: 0.0003207 × height^0.3 × weight(g)^(0.7285 − 0.0188 × log10 weight(g))
Height is in centimetres and weight in kilograms except in the Boyd formula, which uses weight in grams. Mosteller is popular because it is simple; Du Bois is historically common in adults; Haycock is often used in paediatrics. This tool is not a dosing instruction.
| Symbol | Meaning |
|---|---|
| BSA | Body surface area in square metres. |
| height | Standing height in centimetres. |
| weight | Body weight in kilograms (grams for Boyd). |
Mosteller: √(175 × 70 ÷ 3600) = √3.403 = 1.84 m². Du Bois gives 1.85 m², Haycock 1.85 m² and Boyd about 1.85 m². The formulas agree within about 1% at this size.
Surface area grows more slowly than volume as an object gets larger, which is why small bodies have proportionally more skin per kilogram. That relationship matters for heat loss, drug distribution and physiological scaling. The early BSA formulas were built by measuring body surface directly or by modelling the body as a set of geometric shapes. Modern formulas are empirical fits to those measurements. None is exactly right for every body, and all are less reliable in infants, very tall adults and people with severe obesity. In research, BSA is often used to index cardiac output and glomerular filtration rate. In clinical practice, it is one of several size descriptors. If you are comparing your result across time, pick one formula and stick with it, because switching formulas can create a change that looks real but is only arithmetic.
Continue with the ABSI Calculator (A Body Shape Index), Adjusted Body Weight Calculator, or the BAI Calculator (Body Adiposity Index) — or browse more body measurements tools and all health calculators.
Also see the Body Fat Calculator.
There is no universal winner. Mosteller is widely used for its simplicity, Du Bois for historical adult data, and Haycock in paediatric practice. The differences are usually small in adults but can matter in infants.
Every result is a screening estimate from published anthropometric equations, not a diagnosis or a measurement of body composition. Tape measurements should be taken snugly against the skin without compressing it, at the landmarks named in each tool. Equations were derived in specific populations and can be less accurate for athletes, older adults, children, pregnant people and people with significant oedema.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
Content updated: September 2026