Free assessment tool
Body surface area calculator
Calculate body surface area (BSA) with the Mosteller formula from height and weight — enter metric or imperial units and see the full square-root setup behind the answer, not just the number. Free, no signup, runs in your browser.
Interactive calculator
Body surface area (BSA) calculator
Enter height and weight — in metric or imperial units — to calculate body surface area with the Mosteller formula, and see the worked setup below. Results update as you type.
Result
Enter height and weight to see the BSA and the worked setup.
For education and practice only. This tool is a study aid, not a substitute for clinical judgment, a drug reference, or institutional policy. BSA-based dosing (such as chemotherapy) requires an independent double-check before administering.
How it works
The Mosteller formula
Published by Mosteller in 1987, this is the simplest and most widely used BSA equation — a single square root that is easy to compute at the bedside and agrees closely with the older Du Bois formula.
Body surface area (m²)
BSA = √((height cm × weight kg) ÷ 3600)
Multiply height in centimeters by weight in kilograms, divide by 3600, and take the square root. The result is in square meters, usually reported to two decimals.
Unit conversions
cm = in × 2.54 · kg = lb ÷ 2.2
The formula needs centimeters and kilograms. If height is in inches or weight is in pounds, convert first — this calculator does it for you and shows the conversion in the worked steps.
Worked example
A BSA calculation, step by step
The patient
An adult who is 180 cm tall and weighs 80 kg. What is the body surface area?
The setup
- 1. Multiply: 180 cm × 80 kg = 14,400.
- 2. Divide by 3600: 14,400 ÷ 3600 = 4.
- 3. Take the square root: √4 = 2.0.
Answer: 2.0 m².
Reading the result
A BSA of 2.0 m² is at the upper end of the typical adult range of about 1.5–2.0 m². For a BSA-dosed drug ordered at, say, 100 mg/m², this patient’s dose would be 100 × 2.0 = 200 mg.
Enter 180 cm and 80 kg in the calculator above to see this exact worked setup returned. Try imperial units too — 71 in and 176 lb land close to the same BSA.
This clean whole-number result is a good self-check that the formula and the calculator agree.
Common questions
Body surface area, explained
- How do you calculate body surface area with the Mosteller formula?
- BSA in m² equals the square root of (height in cm × weight in kg) divided by 3600: BSA = √((height × weight) ÷ 3600). Convert height to centimeters (inches × 2.54) and weight to kilograms (pounds ÷ 2.2) first if needed, multiply them, divide by 3600, and take the square root.
- Why is body surface area used instead of just weight?
- BSA reflects both height and weight, so it tracks metabolic size and organ function better than weight alone for some drugs. It is used to dose certain medications — chemotherapy is the classic example — and to normalize measurements such as cardiac index. For most everyday drugs, weight-based (mg/kg) dosing is used instead.
- What is a normal adult body surface area?
- Average adult BSA is roughly 1.7 m², with most adults falling between about 1.5 and 2.0 m². Values vary with height and build, so there is no single 'correct' number — it is simply a size measure used in dosing and physiologic calculations.
- Is the Mosteller formula the only BSA equation?
- No. Several equations exist — Du Bois, Haycock, Gehan-George, and others — and they give slightly different results. Mosteller is the most widely used because it is a simple square root that is easy to compute and agrees closely with the older Du Bois formula.
- Can I enter feet and inches or pounds?
- Enter height in centimeters or total inches, and weight in kilograms or pounds — this calculator converts to metric internally (inches × 2.54, pounds ÷ 2.2) and shows the conversion in the worked steps. Convert feet-and-inches to total inches first (for example, 5 ft 11 in = 71 in).
- Is this BSA calculator free and mobile-friendly?
- Yes. It is completely free, needs no account, and runs entirely in your browser, so it works on a phone. It is a study and practice aid only — BSA-based dosing requires an independent double-check against the order and institutional policy before administering.
Put the number to work
From BSA to a safe dose
BSA is a size measure; turning it into a dose is where the med-math happens. Use the full dosage calculator for BSA- and weight-based dosing, read the dosage study guide, or explore the other free calculators.
This calculator and all study material on this site are provided for practice and study only — they are not medical advice or a substitute for clinical judgment, a drug reference, or institutional policy. Verify every dose before administering. NCLEX® is a registered trademark of the National Council of State Boards of Nursing, Inc. (NCSBN), which does not endorse or sponsor this site.