Body Surface Area (BSA) Calculator
Estimate your Body Surface Area from height and weight using the Mosteller and Du Bois formulas — often used for medical dosing.
For information only. Clinical dosing decisions should be made by a qualified professional.
What Is Body Surface Area
Body Surface Area, or BSA, is an estimate of the total surface area of the human body, measured in square metres. A BSA Calculator works out this value from your height and weight, giving a single number that doctors and pharmacists use widely.
BSA is important because it often predicts how the body handles medicines better than weight alone. Many drug doses, especially in cancer treatment and paediatrics, are calculated per square metre of body surface. BSA is also used to assess kidney function, cardiac output and burn coverage. This tool provides an estimate for reference; it is not medical advice, and dosing decisions must be made by a qualified clinician.
How It Works
Several formulas exist, and this calculator shows two of the most trusted:
- Mosteller: BSA = the square root of (height in cm times weight in kg, divided by 3600). It is simple and quick, which is why it is popular in clinics.
- Du Bois: BSA = 0.007184 times height in cm to the power 0.725 times weight in kg to the power 0.425. It is one of the oldest and most cited formulas.
Both use only height and weight, and they usually agree closely. The Mosteller formula is easier to compute by hand, while the Du Bois formula has a long history in medical literature. The calculator displays both so you can compare.
Worked Example
Consider a person who is 170 cm tall and weighs 70 kg. Using Mosteller: 170 times 70 = 11900, divided by 3600 = 3.306, and the square root of that is about 1.82 m^2. Using Du Bois: 0.007184 times 170 to the power 0.725 times 70 to the power 0.425 works out to about 1.81 m^2. The two methods land within a hundredth of a square metre, which is typical. Always treat the result as an estimate, not medical advice.
Why BSA Matters in Medicine
Dosing by body surface area aims to account for differences in metabolism and organ size more fairly than weight alone. In chemotherapy, for instance, the dose of many agents is prescribed in milligrams per square metre, so an accurate BSA directly affects the amount of drug given. Getting it wrong can mean too little effect or too much toxicity.
BSA also appears in formulas for cardiac index, where heart output is divided by BSA, and in estimating fluid needs for burn patients. Because the value feeds into important clinical decisions, it should be calculated carefully and confirmed by the treating team. This calculator is a convenient reference tool, but it does not replace professional judgement or local dosing protocols.
Frequently Asked Questions
For an average adult, BSA is roughly 1.7 to 2.0 square metres, with men often slightly higher than women. Children have smaller values that grow with height and weight. The exact figure depends on your own measurements.
Both are widely accepted and usually give very similar results. Mosteller is simpler and common in everyday clinical use, while Du Bois is a long-standing reference. Your hospital may specify which to follow.
BSA tends to track metabolism and organ size better than weight alone, so many medicines, particularly chemotherapy, are dosed in milligrams per square metre to give safer, more consistent results across patients.
Yes. Because the formulas use weight, a change in weight changes your BSA. Height has a larger fixed influence, but notable weight changes will shift the result and may affect weight-based or surface-based dosing.
It gives a reliable estimate using standard formulas, but it is for reference only. Clinical dosing must be confirmed by a doctor or pharmacist following approved protocols and the patient assessment.
The same formulas apply to children, and BSA is often used in paediatric dosing. However, paediatric care is sensitive, so any dose based on BSA must be set and checked by a qualified clinician.