Body surface area (BSA): what it is and how to calculate it
Body surface area (BSA) estimates the total surface area of the human body (in m²). In many medical settings, BSA is used as an input for dose calculations, renal function estimates, and other clinical references.
This guide explains what BSA is, how it’s calculated, and what to watch out for.
Quick BSA calculator (cm/in + kg/lb)
Use our free calculator to compute BSA from height and weight:
BSA formulas (Mosteller vs Du Bois)
There are multiple formulas because they were derived from different data and trade-offs (simplicity vs fit).
Two common ones you’ll see:
- Mosteller (popular because it’s simple)
- Du Bois / DuBois (older but widely referenced)
In most everyday use, different formulas produce close values, but if you’re using BSA for a clinical protocol, follow the formula specified by that protocol.
How to enter measurements correctly
BSA depends on height and weight, so measurement quality matters:
- Use consistent units (cm + kg, or in + lb).
- If your scale fluctuates, use a weekly average instead of a single reading.
- If you’re using BSA for a medical decision, double-check the inputs.
How to interpret BSA (and what it is not)
BSA is:
- A scaling factor used in many medical calculations.
- A way to normalize some values between people of different sizes.
BSA is not:
- A direct measure of body fat or fitness.
- A substitute for diagnosis or dosing guidance from your clinician.
Useful pairings (BSA + other references)
Depending on why you’re calculating BSA, these tools can add context: