Body Surface Area (BSA) Calculator

Calculate body surface area with established clinical formulas for dosing and assessment.

Calculate BSA

Choose a formula, then enter height and weight in metric units.

Calculation formula

Height (cm)

Weight (kg)

About body surface area

Body surface area, abbreviated BSA, estimates the total external surface of a person's body. It is expressed in square meters and combines height and weight into a value that often reflects metabolic mass more consistently than body weight alone. Clinicians use BSA in several settings, including the calculation of some chemotherapy doses, cardiac index, kidney function normalization, burn care, and pediatric medication protocols. It is an estimate rather than a direct physical measurement. Several equations are available because researchers developed formulas from different study populations. The Mosteller formula takes the square root of height in centimeters multiplied by weight in kilograms and divided by 3600. Its simplicity makes it common in clinical practice. The DuBois and DuBois equation is older and uses fractional powers of height and weight. Haycock was derived with broader representation of infants and children, while Boyd uses weight in grams and a logarithmic weight exponent. The formulas usually give similar adult results, but differences can become meaningful at very small or very large body sizes. Always use the method required by the medication label, institution, trial, or clinical protocol. Switching formulas during a course of treatment can introduce an unintended dose difference. Some oncology protocols also cap the BSA used for dosing, while others specifically advise against capping it. This calculator reports the mathematical estimate only and does not apply dose limits, rounding rules, renal adjustments, or disease-specific modifications. Measure height without shoes and weight with calibrated equipment when accuracy matters. Fluid retention, amputation, pregnancy, severe obesity, and rapidly changing weight may require specialized judgment. A calculated BSA does not itself recommend a drug dose and should never replace verification by a pharmacist or prescribing clinician. If a result will affect treatment, confirm the source measurements, selected equation, units, significant digits, and current protocol before use.

BSA examples

Height and weight	Mosteller BSA	Typical context
170 cm, 70 kg	1.82 m²	Average adult example
180 cm, 80 kg	2.00 m²	Exact square-root example
100 cm, 20 kg	0.75 m²	Pediatric-sized example

How to calculate BSA

Select the formula required by your clinical or educational protocol.
Measure and enter height in centimeters.
Measure and enter weight in kilograms.
Select Calculate BSA and verify the formula, units, and result before use.

Frequently asked questions

Which BSA formula should I use?

Use the formula named by the relevant medication, institution, or study protocol. Mosteller is widely used because it is simple, but another equation may be required for a specific population.

Why do the formulas give different results?

Each equation was fitted to measurements from a particular sample and uses different exponents. Differences are often small in average adults and can grow at body-size extremes.

Can BSA determine a medication dose?

BSA can be one input in a prescribed dosing equation, but it does not determine a safe dose by itself. Drug-specific limits, organ function, laboratory results, and professional verification remain necessary.

Is BSA the same as BMI?

No, BSA estimates external body surface in square meters. BMI relates weight to squared height and is mainly used as a body-size screening category.

Should BSA be capped at 2 square meters?

That practice depends on the drug and protocol and is not a universal rule. Follow current prescribing guidance rather than applying an automatic cap.