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What body surface area is
Body surface area (BSA) is the total external area of your body, expressed in square metres. It's used far more in medicine than in everyday fitness, because many physiological processes scale with surface area rather than with body weight.
The average adult has a BSA of about 1.7 m². Clinicians use it to size medication doses (especially chemotherapy), calculate cardiac index, estimate fluid requirements and assess metabolic rate.
The formulas we use
BSA can't be measured directly, so it's estimated from height and weight. This calculator shows three validated formulas:
- Mosteller — √(height × weight / 3600). Simple, accurate and the most widely used today; we show it as the headline result.
- Du Bois & Du Bois — the classic 1916 formula still referenced throughout medicine.
- Haycock — well suited to a wide range of body sizes, including children.
The three usually agree within a few percent of each other.
Why BSA beats body weight for dosing
Many drugs and physiological measures track surface area more closely than mass. Two people can weigh the same but have different surface areas depending on height, and dosing by BSA gives a more consistent exposure across different body shapes. That's why oncology and paediatric doses are so often written "per m²".
Limits to keep in mind
This tool is for general education. It is not a substitute for a clinician's calculation, and you should never adjust any medication dose based on it. If a BSA figure matters for your care, your healthcare team will calculate and verify it.
Helpful tools
Track weight and trends that feed into BSA over time.
View options →Get an accurate height reading at home.
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Frequently asked questions
What is the average body surface area?
An average adult has a BSA of roughly 1.7 m². Women tend to be slightly lower and men slightly higher, depending on height and weight.
Which BSA formula is most accurate?
The Mosteller formula is the most widely used because it's simple and reliably accurate for adults, which is why we show it as the main result.
Why is BSA used for medication doses?
Many drugs distribute and clear in proportion to surface area rather than weight, so dosing per m² gives more consistent exposure across different body sizes.
Is BSA the same as body fat?
No. BSA measures the area of your body's surface, while body fat percentage measures how much of your weight is fat. They are unrelated metrics.