Body Surface Area (BSA) Calculator
Find your body surface area from your height and weight, in square metres and square feet, and compare every common formula.
Pick any unit for each, for example feet and inches with kilograms.
Every formula side by side
| Formula | m² | ft² | vs main |
|---|
For clinicians
For clinicians only. Always follow the protocol and a pharmacist's check. Never work out or change a dose for yourself or someone else from this page.
How your BSA is worked out
Your numbers, step by step, with the formula you picked.
- 1
Height and weight
170 cm, 70 kg
- 2
Multiply them
170 × 70 = 11,900
- 3
Divide and square root
√(11,900 ÷ 3,600)
- 4
Your body surface
1.82 m² = 19.6 ft²
Read more: every formula, a worked example and notes
Body surface area (BSA) is the area of the outside of your body. Measuring it directly is hard, so it is estimated from height and weight. Doctors use it to scale some medicine doses (mg per m²), to compare heart output between people (cardiac index) and to scale kidney test results to an average adult of 1.73 m².
General information, not medical advice. Medicine doses are set by a doctor and checked by a pharmacist using the protocol for that drug.
The formula
Mosteller (used by default): BSA in m² = square root of (height in cm × weight in kg ÷ 3,600)
In inches and pounds Mosteller is √(inches × pounds ÷ 3,131). Square feet = m² × 10.7639. The other formulas raise weight and height to different powers and multiply by a constant (height in cm, weight in kg, Boyd uses weight in grams):
| Formula | BSA in m² = | Notes |
|---|---|---|
| Mosteller (1987) | √(height cm × weight kg ÷ 3600) | the most used today; simple and good for adults and children |
| Du Bois (1916) | 0.007184 × kg^0.425 × cm^0.725 | the classic formula, still common in labs and research |
| Haycock (1978) | 0.024265 × kg^0.5378 × cm^0.3964 | made with children and babies; often used in paediatrics |
| Gehan & George (1970) | 0.0235 × kg^0.51456 × cm^0.42246 | from a large data set; used in some cancer protocols |
| Boyd (1935) | 0.0003207 × cm^0.3 × grams^(0.7285 − 0.0188 × log₁₀ grams) | fits a wide range of body sizes, from babies up |
| Fujimoto (1968) | 0.008883 × kg^0.444 × cm^0.663 | made with Japanese adults |
| Takahira (1925) | 0.007241 × kg^0.425 × cm^0.725 | made with Japanese people; Du Bois shape |
| Shuter & Aslani (2000) | 0.00949 × kg^0.441 × cm^0.655 | a modern refit of Du Bois’s data |
| Schlich (2010) | women 0.000975482 × kg^0.46 × cm^1.08; men 0.000579479 × kg^0.38 × cm^1.24 | separate for women and men; from adult 3D body scans |
Dose helper: total dose = dose per m² × BSA, with the BSA rounded to 2 decimals and capped if you set a cap. Cardiac index = cardiac output (L/min) ÷ BSA; about 2.5–4.0 L/min/m² is normal at rest.
Worked example
A woman 170 cm tall weighing 70 kg. Mosteller: 170 × 70 = 11,900; 11,900 ÷ 3,600 = 3.3056; √3.3056 = 1.8181, shown as 1.82 m². In square feet: 1.8181 × 10.7639 = 19.57 ft².
Du Bois for the same person: 70^0.425 = 6.0837 and 170^0.725 = 41.4072, so 0.007184 × 6.0837 × 41.4072 = 1.81 m² (1.8097). The average of all 9 formulas is 1.81 m², from 1.76 (Fujimoto) to 1.83 (Boyd). Her BMI is 70 ÷ (1.7 × 1.7) = 24.2.
If a protocol said 75 mg/m², the total would be 75 × 1.82 = 136.5 mg. With a cardiac output of 5 L/min, her cardiac index is 5 ÷ 1.8181 = 2.75 L/min/m², in the normal range.
Typical BSA by body size (Mosteller)
| Example | Height, weight | BSA |
|---|---|---|
| Newborn baby | 50 cm, 3.5 kg | 0.22 m² |
| Toddler (about 2 years) | 87 cm, 12 kg | 0.54 m² |
| Child (about 10 years) | 140 cm, 35 kg | 1.17 m² |
| Adult woman | 162 cm, 62 kg | 1.67 m² |
| Adult man | 176 cm, 80 kg | 1.98 m² |
Notes
- Sources: Mosteller, NEJM 1987; Du Bois and Du Bois, Archives of Internal Medicine 1916; Haycock and others, Journal of Pediatrics 1978; Gehan and George, Cancer Chemotherapy Reports 1970; Boyd, 1935; Fujimoto and others, 1968; Takahira, 1925; Shuter and Aslani, European Journal of Applied Physiology 2000; Schlich and others, Nutrition and Metabolism 2010. Coefficients checked on 13 October 2026.
- Schlich was made from adult body scans, so it is left out of the average for under-18s. For children, Mosteller and Haycock are the usual choices.
- For very large or very small people the formulas spread further apart. Some protocols cap BSA (often at 2.0 m²) or use an adjusted weight; follow the protocol.
- Height and weight should be measured, not guessed: a 5 kg error changes BSA by about 3–4%.
Common questions
What is body surface area?
Body surface area (BSA) is the total area of the outside of your body, in square metres (m²). It can't easily be measured, so it is estimated from height and weight with a formula. A typical adult is about 1.6 to 2.0 m²; 1.73 m² is the standard "average adult" that kidney test results (eGFR) are scaled to.
How do you calculate BSA?
The most used formula is Mosteller: multiply your height in cm by your weight in kg, divide by 3,600 and take the square root. For 170 cm and 70 kg that is √(170 × 70 ÷ 3,600) = √3.3056 = 1.82 m².
Which BSA formula is best?
For most adults the formulas agree within a few percent. Mosteller is the most used because it is simple and works well for adults and children; Du Bois is the classic one; Haycock and Boyd were built with children and babies included. Hospitals and drug protocols usually say which one to use, so follow that.
Why do doctors use BSA for drug doses?
Some medicines, many cancer drugs among them, are dosed per square metre of body surface (mg/m²) because BSA tracks blood volume and how fast the body clears the drug better than weight alone. The dose per m² is multiplied by the BSA. Only a doctor and pharmacist set and check a dose, often with a cap on BSA for very large people.
What is cardiac index?
Cardiac index is cardiac output (litres of blood the heart pumps each minute) divided by BSA, so it can be compared between people of different sizes. A normal resting value is about 2.5 to 4.0 L/min/m². It is measured in hospital, for example with an echocardiogram or a heart catheter.
Is BSA the same as BMI?
No. BMI (weight ÷ height²) is a screening number for weight. BSA is an area in m² used to scale doses and body measurements. Two people with the same BMI can have quite different BSAs because a taller person has more skin.
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