A body surface area calculator estimates the total outer surface of the body in square meters from height and weight, here using the Mosteller formula. A person who weighs 70 kg and is 175 cm tall has a BSA of about 1.84 m².
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How to use the body surface area calculator
- Enter weight in kilograms.
- Enter height in centimeters.
- Read the body surface area in m².
What formula does the body surface area calculator use?
- Mosteller (1987): BSA (m²) = √(height in cm × weight in kg ÷ 3,600)
- In pounds and inches: BSA = √(height in in × weight in lb ÷ 3,131)
- Du Bois (1916), for comparison: BSA = 0.007184 × weight0.425 × height0.725
The body surface area calculator uses the Mosteller formula, published as a simplified alternative to older equations and now the most widely used in clinical practice. For most adults the formulas agree within a few hundredths of a square meter.
Body surface area calculator worked example
| Weight | Height | Mosteller | Du Bois |
|---|---|---|---|
| 70 kg | 175 cm | 1.84 m² | 1.85 m² |
| 60 kg | 160 cm | 1.63 m² | 1.62 m² |
| 90 kg | 185 cm | 2.15 m² | 2.14 m² |
| 50 kg | 165 cm | 1.51 m² | 1.53 m² |
| 110 kg | 180 cm | 2.35 m² | 2.29 m² |
| 20 kg | 110 cm | 0.78 m² | 0.78 m² |
For a person who weighs 70 kg and is 175 cm tall, height × weight = 12,250. Divided by 3,600 that is 3.403, and the square root is about 1.845 m². The Du Bois formula gives about 1.848 m² for the same person. A typical adult has a BSA of roughly 1.6 to 2.0 m².
Why body surface area is used
Body surface area estimates the outer surface of the body and tracks metabolic size better than weight alone. Doctors use it to calculate doses of many chemotherapy drugs, which are often prescribed in milligrams per square meter, and to scale some measurements, such as cardiac index (cardiac output divided by BSA) and kidney filtration rates. It is also used in burn care and in some drug trials to compare doses across body sizes.
Entering the right units
- Weight must be in kilograms: divide pounds by 2.2046.
- Height must be in centimeters: multiply inches by 2.54.
- A 154 lb, 5 ft 9 in person is about 70 kg and 175 cm, which gives the 1.85 m² example above.
Limits of BSA formulas
All BSA formulas are estimates derived from small groups of people. They can differ more for very small children and for people with very high or very low body weight, and clinicians sometimes cap doses or use adjusted weights in those cases. Different formulas give slightly different answers, so a medical team will use the one specified in its protocol. This body surface area calculator is for general information and must not be used on its own to set or change a medication dose; only your clinician can do that.
BSA versus BMI
Body mass index (weight in kg divided by height in meters squared) screens for underweight and overweight. BSA measures overall body size for scaling doses and physiology. They answer different questions, so one cannot be converted into the other.
BSA in children and in dosing
Children have more surface area relative to their weight than adults. A child who weighs 20 kg and is 110 cm tall has a Mosteller BSA of about 0.78 m², roughly 40% of a typical adult’s, even though their weight is under a third of the adult’s. This is one reason doses based on body surface area and doses based on weight can differ for the same child. Pediatric teams follow published dosing references and their own protocols, and they check calculations independently before a drug is given.
In cancer care, a dose written as 100 mg/m² means 100 mg multiplied by the patient’s BSA, so a patient with a BSA of 1.85 m² would receive 185 mg. Measured height and weight should be current, because weight loss during treatment changes the result. Use the body surface area calculator to understand where a number on a treatment plan comes from, and ask your care team if your figures look different, since they may use another formula or an adjusted weight.
Related converters and calculators
Related calculators:
- BMI calculator: BMI
- Ideal weight calculator: weight
- BMR calculator: metabolism
- Body fat calculator: body composition
Sources
Mosteller RD. Simplified calculation of body-surface area. N Engl J Med 1987;317:1098; National Cancer Institute Thesaurus: Mosteller body surface area formula.
Questions about this calculator
What is the Mosteller formula?
BSA = √(height cm × weight kg ÷ 3,600).
What is a normal body surface area?
Most adults are roughly 1.6 to 2.0 m².
What is BSA used for?
Chemotherapy dosing, cardiac index and scaling other measurements.
Which BSA formula is best?
Mosteller is the most widely used; results are close to Du Bois for most adults.
Can I use this to dose medicine?
No. Dosing must be done by your clinician.
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
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