Body surface area calculator (Mosteller)
Body surface area (BSA) estimates the total area of your skin in square meters, and it is the number clinicians most often use to size doses of chemotherapy and certain other drugs. This calculator uses the Mosteller formula, the simplest and most widely used method in US oncology practice. A typical adult BSA is around 1.7 m² (roughly 1.7 for women and 1.9 for men).
How it works
The Mosteller formula multiplies your height by your weight, divides by a fixed constant, and takes the square root of the result. In metric units, BSA in m² equals the square root of (height in cm × weight in kg ÷ 3600). If you prefer US units, the equivalent is the square root of (height in inches × weight in pounds ÷ 3131) — the different constant just accounts for the unit conversion, so both give the same answer. That single square-root step is the whole method; there are no age, sex, or body-fat adjustments built in.
Worked example
Take an adult who is 175 cm tall and weighs 75 kg. Multiply: 175 × 75 = 13,125. Divide by 3,600: 13,125 ÷ 3,600 = 3.65. Take the square root: √3.65 ≈ 1.91 m². The same person in US units (about 68.9 in and 165 lb) gives √(68.9 × 165 ÷ 3131) ≈ 1.91 m², matching the metric result.
Important
This tool gives an estimated body surface area (BSA) for general education only — it is not medical advice and must not be used to calculate, start, stop, or change any medication dose. It applies the Mosteller formula for ADULTS only; do not use it for infants, children, or pregnancy, where dosing follows entirely different rules. BSA is just one input into a dose. Choosing, calculating, adjusting, and independently double-checking any drug dose — especially chemotherapy, where a small BSA error can cause serious harm — is the job of a licensed clinician and pharmacist, not a calculator. Doses should be based on actual measured and verified height and weight, not self-reported figures; a typo here changes the result. Many cancer centers cap or adjust BSA-based doses in patients with obesity or at the extremes of body size, so a raw BSA from this tool may not match (and should not override) what your care team uses. If your result differs from what your care team calculated, trust your care team and ask them — never act on the number shown here.