Body Surface Area (BSA) Calculator
Calculate your body surface area (BSA) in m² from height and weight across eight formulas — Du Bois, Mosteller, Haycock, Gehan & George, Boyd, and more.
Body surface area (BSA) is the total external area of your body, expressed in square metres (m²). It’s used far more in medicine than in fitness: chemotherapy and many other drugs are dosed per m², and measures like the cardiac index are “indexed” to BSA so they can be compared fairly between a small and a large person.
Eight formulas, one measurement
You can’t measure surface area directly, so it’s estimated from height and weight. This calculator runs eight established equations at once:
- Du Bois & Du Bois (1916) — the original and still the reference standard.
- Mosteller (1987) — the simplest (a square-root formula) and the most used clinically today.
- Haycock (1978) — developed with children in mind, accurate across ages.
- Gehan & George (1970) — derived from a large sample of direct measurements.
- Boyd (1935) — an older equation with a weight-dependent exponent.
- Fujimoto (1968) and Takahira (1925) — derived from Japanese populations.
- Schlich (2010) — a modern, sex-specific equation (the only one here that uses sex).
For a typical adult they land within a couple of percent of each other. We show Du Bois as the headline and list the rest so you can match whichever your clinician or protocol uses.
How to calculate BSA by hand (the Mosteller formula)
If you want to work it out yourself, Mosteller’s is the one to reach for — it’s a single square root:
BSA (m²) = √( height(cm) × weight(kg) ÷ 3600 )
So a person 175 cm and 70 kg has a BSA of √(175 × 70 ÷ 3600) = √3.40 ≈ 1.84 m². The other seven equations add small refinements, but this is the version most clinicians reach for at the bedside. The calculator itself works in either unit system — enter 5 ft 9 in and 154 lb instead of 175 cm and 70 kg and it converts automatically before applying the same equation.
Typical values
An average adult is around 1.7 m² — closer to 1.9 m² for a taller, heavier man and 1.6 m² for a smaller woman. Because BSA depends on both height and weight, two people of the same weight can have noticeably different values.
| Group | Approx. BSA |
|---|---|
| Newborn | 0.25 m² |
| 2-year-old | 0.5 m² |
| 9-year-old | 1.07 m² |
| 10-year-old | 1.14 m² |
| Adult woman | 1.6 m² |
| Adult man | 1.9 m² |
A reference, not a prescription
This tool is for education and quick reference. Never use it to set your own medication dose — clinical dosing accounts for organ function, drug, and protocol factors this calculator doesn’t model.
Frequently asked questions
What is body surface area used for?
Body surface area (BSA) is the total surface area of the human body, in square metres. Clinicians use it to dose many drugs — especially chemotherapy — and to index measurements like cardiac output (the cardiac index) and glomerular filtration rate, because these scale better with surface area than with bodyweight.
How do you calculate body surface area?
The simplest method is the Mosteller formula: BSA (m²) = the square root of (height in cm × weight in kg ÷ 3600). A person 175 cm and 70 kg has a BSA of about 1.84 m². This calculator runs Mosteller alongside seven other equations so you can match whichever your protocol uses.
Which BSA formula should I use?
The Mosteller formula is the most common in clinical practice because it's simple and accurate, while Du Bois & Du Bois (1916) is the historic reference the others are compared against. For most people all eight formulas agree to within a few percent, which is why we show them side by side.
What is a normal body surface area?
An average adult has a BSA of roughly 1.7 m² — about 1.9 m² for men and 1.6 m² for women. Children are much lower; the figure rises with both height and weight.
Is BSA better than weight for drug dosing?
For some drugs, yes. Dosing by surface area accounts for differences in metabolism and blood volume that track surface area more closely than weight alone. Always follow a clinician's dosing — this calculator is for reference and education.
References
- Du Bois D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med. 1916
- Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987
- Haycock GB, et al. Geometric method for measuring body surface area. J Pediatr. 1978
- Gehan EA, George SL. Estimation of human body surface area from height and weight (Cancer Chemother Rep, 1970)