What is body surface area, and why would anyone calculate it?
Body surface area is exactly what it sounds like: the total area of your skin, expressed in square metres. A typical adult comes out around 1.7 m² — roughly the footprint of a single bed. It sounds like trivia until you learn where it's used: BSA turns out to track metabolic processes better than body weight does, which made it medicine's preferred scaling factor for some very consequential math.
Chemotherapy doses are the famous example — most are prescribed in milligrams per square metre. Cardiac output is normalised by BSA to give the cardiac index, kidney function is reported against a standard 1.73 m² body, and burn severity is described as a percentage of BSA. If you've ever seen 'mg/m²' on a prescription and wondered where the m² came from, this calculator is the answer.
The four BSA formulas compared
Nobody unrolls your skin and measures it, of course — BSA is estimated from height and weight. The oldest estimate still in daily use is remarkable: Du Bois and Du Bois derived their 1916 formula from direct measurements of just nine people, and it's still cited over a century later. The Mosteller formula (1987) is the modern favourite because it's simple enough to do in your head with a square root key: the square root of height times weight divided by 3,600.
For someone 170 cm and 70 kg, Mosteller gives √(170 × 70 ÷ 3,600) ≈ 1.82 m². Haycock and Gehan & George — both built from larger and more diverse samples, including children — land within a few percent of the same answer. The calculator runs all four and averages them, and the spread between them is usually smaller than the day-to-day change in your own weight.
BSA pairs naturally with the GFR calculator — kidney function is standardised to a 1.73 m² body — and with the BMI calculator for the more familiar height-weight measure.
Typical BSA values
| Group | Typical BSA |
|---|---|
| Newborn | ≈ 0.25 m² |
| Child, ~10 years | ≈ 1.14 m² |
| Adult woman | ≈ 1.6 m² |
| Adult man | ≈ 1.9 m² |
| Clinical standard body | 1.73 m² |
A note for any clinical use: dosing calculations belong to prescribers. Hospitals often mandate a specific formula precisely because the estimates differ slightly — this page is for understanding the number, not acting on it.
Frequently asked questions about BSA
What is body surface area used for?
BSA appears in clinical dosing (especially chemotherapy), cardiac index calculations, and metabolic research.
Which BSA formula is best?
Mosteller is widely used for simplicity. Du Bois is classic. Formulas differ slightly — clinical settings often specify one.
How do I use this BSA calculator?
Enter height and weight, choose units, and click Calculate to compare BSA formulas.
Sources and further reading
- Mosteller RD — Simplified calculation of body-surface area (NEJM, 1987)
- Du Bois D, Du Bois EF — A formula to estimate the approximate surface area (1916, reprinted)
- National Cancer Institute — Body surface area definition
This page is for general information only and is not medical advice. Drug dosing must always be performed by qualified clinicians.