How the Mosteller formula works
The Mosteller formula is wonderfully simple: BSA = √(height × weight ÷ 3600), with height in cm and weight in kg. At 180 cm and 80 kg you get √(14400 ÷ 3600) = √4 = 2.0 m². Pair it with the lean body mass calculator for a fuller body picture. The same height and weight inputs also drive the BMI calculator.
What BSA is used for
Body surface area is a size measure that scales better than weight alone for some physiological comparisons. This is a general wellness estimate, not medical advice. Talk to a healthcare professional for personal guidance.
Surface area grows more slowly than weight, so it scales dosing, heat exchange and metabolic comparisons better than kilograms alone: a person twice as heavy does not have twice the surface area. That is why BSA appears in some drug dosing and cardiac index calculations rather than body weight. For dosing decisions clinicians often look at lean tissue too, via the lean body mass calculator.
Estimate, not measurement
BSA cannot be measured directly in everyday settings, so formulas like Mosteller are the standard estimate. Different formulas (Du Bois, Haycock) give slightly different numbers. Compare with the ideal weight calculator for context.
Du Bois tends to read slightly lower at the extremes of height and weight, while Haycock was developed with children in mind. The spread is usually under 5%, so the choice rarely changes the practical picture. Enter height in centimetres and weight in kilograms; mixing units, such as typing 1.8 for height, is the quickest way to get an impossible answer. A reference weight for a given height comes from the ideal weight calculator.
Frequently asked questions
- What is body surface area?
- A measure of the total external area of your body, expressed in square metres.
- Which formula is used here?
- The Mosteller formula, valued for being simple and reasonably accurate.
- What is a typical BSA?
- Most adults fall between about 1.5 and 2.0 m², depending on height and weight.
- Why do formulas give different results?
- Mosteller, Du Bois and Haycock use different math, so figures differ slightly.
- Do I enter height in centimetres or metres?
- Centimetres. The Mosteller formula divides height in cm multiplied by weight in kg by 3600, so entering 1.8 instead of 180 returns a result roughly ten times too small.