Body surface area is calculated from height and weight: Formula, Uses, and Limits

Body surface area (BSA) is an estimate of the external surface area of the body, commonly expressed in square metres. A BSA calculator uses height and weight to produce a mathematical estimate. Clinicians may refer to BSA in specific settings, but an online result is not a measurement of body composition and must not be used independently to choose or adjust medication.

The Mosteller formula

One commonly used equation is:

BSA (m²) = √[height (cm) × weight (kg) ÷ 3600]

For example, using illustrative measurements of 170 cm and 70 kg gives √(170 × 70 ÷ 3600), or about 1.82 m². This example demonstrates the arithmetic only. It is not a dose recommendation or an assessment of an individual’s health. The original Mosteller publication described a simplified calculation of body-surface area.

Body surface area infographic showing height and weight entered into the Mosteller equation to estimate square metres; not a medication dose. — Original formula explainer. Example values are illustrative; clinical dosing decisions require a qualified professional.

Why estimates can differ

Several BSA equations exist, and they may give slightly different estimates. Results also depend on using the required units correctly. Confirm that height is in centimetres and weight is in kilograms when using the formula above. If you enter inches or pounds without conversion, the answer will not be valid.

BSA is not the same as BMI, body-fat percentage, or a direct scan of body surface. If a treatment uses BSA, clinicians follow the relevant protocol and consider the medicine, indication, other measurements, and patient-specific factors. Never calculate or change a prescription dose from a website result.

For a general overview of body measurements, see the CDC explanation of BMI and screening limits. Our calculator collection is educational and is not a substitute for clinical decisions.

Silent visual explainer. Transcript: the Mosteller equation estimates BSA from height and weight; it is not a body-fat result or a medication instruction.

Common questions

What units does the formula use?

Centimetres for height and kilograms for weight; the result is in square metres.

Is BSA the same as BMI?

No. BMI relates weight to height squared; BSA estimates surface area using a different equation.

Can I use BSA to work out a medicine dose?

No. Do not choose or change a dose using an online calculator. Ask the prescribing healthcare professional.

Sources

Educational information only; not a clinical measurement or medication-dosing recommendation.

Body Surface Area Calculator