Body Surface Area (BSA) Calculator
Calculate body surface area (BSA) from height and weight using common clinical formulas like Mosteller, Du Bois, Haycock, Gehan & George, and Boyd. Includes unit conversion, formula comparison, a simple body-size visual, and clear step-by-step output.
Background
Body surface area estimates the total external surface of the body. In clinical settings, BSA is commonly used for medication dosing, some chemotherapy calculations, burn assessment, and normalizing measures like cardiac index. It is an estimate, so different formulas may give slightly different results.
How to use this calculator
- Choose metric or imperial units.
- Enter your height and weight.
- Pick a primary BSA formula, or keep Mosteller as the default.
- Turn on Compare all formulas to see how several common BSA equations differ.
- Click Calculate to see BSA in m² and ft², plus optional BMI, comparison values, interpretation, and steps.
How this calculator works
- The calculator first converts all inputs into centimeters and kilograms.
- Mosteller is often used because it is simple and widely taught.
- Du Bois, Haycock, Gehan & George, and Boyd are alternative formulas that may produce slightly different estimates.
- The calculator can also show BMI as an extra body-size reference, but BMI and BSA are different measurements.
- This tool provides an estimate and should not replace clinical judgment or dosing protocols.
Formula & Equations Used
Mosteller: BSA = √((height in cm × weight in kg) / 3600)
Du Bois: BSA = 0.007184 × height^0.725 × weight^0.425
Haycock: BSA = 0.024265 × height^0.3964 × weight^0.5378
Gehan & George: BSA = 0.0235 × height^0.42246 × weight^0.51456
Boyd: BSA = 0.0003207 × height^0.3 × weight(g)^(0.7285 − 0.0188·log10(weight(g)))
BMI (optional): BMI = weight(kg) / height(m)^2
Example Problem & Step-by-Step Solution
Example 1 — Mosteller formula
A person is 175 cm tall and weighs 72 kg. Find body surface area using the Mosteller formula.
- Use BSA = √((height × weight)/3600).
- Substitute: BSA = √((175 × 72)/3600).
- Compute the inside value: 12600/3600 = 3.5.
- Take the square root: BSA = √3.5 ≈ 1.87 m².
Example 2 — Imperial inputs using Mosteller
A person is 5 ft 9 in tall and weighs 159 lb. Find body surface area using the Mosteller formula.
- Convert height to centimeters: 5 ft 9 in = 69 in, and 69 × 2.54 = 175.26 cm.
- Convert weight to kilograms: 159 lb ÷ 2.20462 ≈ 72.12 kg.
- Use BSA = √((height × weight)/3600).
- Substitute: BSA = √((175.26 × 72.12)/3600).
- Compute the inside value: (175.26 × 72.12)/3600 ≈ 3.511.
- Take the square root: BSA ≈ √3.511 ≈ 1.87 m².
Example 3 — Pediatric example using Haycock
A child is 110 cm tall and weighs 18 kg. Find body surface area using the Haycock formula.
- Use the Haycock formula: BSA = 0.024265 × height^0.3964 × weight^0.5378.
- Substitute: BSA = 0.024265 × 110^0.3964 × 18^0.5378.
- Evaluate the exponents: 110^0.3964 ≈ 6.45 and 18^0.5378 ≈ 4.73.
- Multiply: BSA ≈ 0.024265 × 6.45 × 4.73.
- Compute the result: BSA ≈ 0.74 m².
Frequently Asked Questions
Q: What is body surface area used for?
BSA is often used in medication dosing, chemotherapy calculations, burn assessment, and for normalizing some clinical measures.
Q: Which BSA formula should I use?
Mosteller is a common student-friendly default. Other formulas like Du Bois, Haycock, Gehan & George, and Boyd may give slightly different estimates.
Q: Is BSA the same as BMI?
No. BSA estimates body surface area, while BMI compares weight to height squared. They describe different things.
Q: Why do formulas give different answers?
Each formula was developed from different data and mathematical fitting methods, so small differences are expected.
