Body Surface Area (BSA) Calculator
Calculate body surface area in square metres (m²) from height and weight. This free BSA calculator uses the Mosteller formula, the most widely used method in clinical practice, and also shows results from the DuBois, Haycock and Gehan-George formulas for comparison.
What is body surface area (BSA)?
Body surface area (BSA) is the total area of the outer surface of the human body, measured in square metres (m²). Because it is very hard to measure directly, doctors estimate it from height and weight using a formula. BSA is considered a better indicator of metabolic size than body weight alone, since it reflects both how tall and how heavy a person is.
What is BSA used for?
BSA is mainly used in medicine as a reference value. Common uses include:
Medication dosing: doses of some drugs, especially chemotherapy medicines, are calculated per square metre of body surface area, because this tends to match how the body processes the drug more closely than weight alone.
Heart measurements: the cardiac index is the heart's output divided by BSA, which allows doctors to compare heart function between people of different sizes.
Kidney function: estimated glomerular filtration rate (eGFR) is usually reported per 1.73 m², a standard adult BSA, so results can be compared across patients.
BSA formulas
Several formulas are used to estimate body surface area. This calculator shows four of the best known, with height in centimetres and weight in kilograms:
Mosteller (1987): BSA = √(height × weight ÷ 3600)
DuBois & DuBois (1916): BSA = 0.007184 × height0.725 × weight0.425
Haycock (1978): BSA = 0.024265 × height0.3964 × weight0.5378
Gehan & George (1970): BSA = 0.0235 × height0.42246 × weight0.51456
Example: For a person who is 170 cm tall and weighs 65 kg, the Mosteller formula gives √(170 × 65 ÷ 3600) = √3.07 = 1.75 m².
Which BSA formula is best?
The Mosteller formula is the most popular today because it is simple, easy to calculate and gives results very close to the older formulas for most adults. The DuBois formula is the oldest and is still widely used, although it was developed from a very small group of people and may be less accurate for children and people with obesity. The Haycock formula was designed to work well for infants and children as well as adults. For most adults, all four formulas give results within a few hundredths of a square metre. Hospitals usually choose one formula and use it consistently.
Average body surface area
| Group | Approximate BSA |
|---|---|
| Newborn | 0.25 m² |
| Child, 2 years | 0.5 m² |
| Child, 10 years | 1.14 m² |
| Adult woman | 1.6 m² |
| Adult man | 1.9 m² |
These are typical values only. Your own BSA depends on your height and weight.
Important note
This calculator is an educational tool. It does not calculate medicine doses, and BSA-based dosing must only be done by doctors, pharmacists or other trained healthcare professionals, who may also adjust doses for kidney function, age and other factors. If you have questions about your treatment, speak with your healthcare team. You may also find our BMI Calculator and Ideal Weight Calculator useful for general health checks.
Frequently Asked Questions
What is a normal body surface area?
There is no single normal value, because BSA depends on height and weight. The average adult BSA is about 1.9 m² for men and about 1.6 m² for women. A value of 1.73 m² is used as a standard adult reference in kidney function tests.
Which formula does this BSA calculator use?
The main result uses the Mosteller formula, which is the most widely used in clinical practice. Results from the DuBois, Haycock and Gehan-George formulas are shown for comparison.
Why is BSA used instead of weight for some medicines?
For some medicines, especially chemotherapy drugs, BSA matches how the body handles the drug more closely than weight alone. Using BSA helps doctors give a more consistent dose to patients of different sizes.
Can I use this calculator for children?
Yes, the formulas work for children, and the Haycock formula was specifically designed to include infants and children. However, any medical use of a child's BSA should be handled by a doctor.
How do I calculate BSA by hand?
Using the Mosteller formula, multiply your height in cm by your weight in kg, divide by 3600, and take the square root. For example, 170 × 65 = 11,050; 11,050 ÷ 3600 = 3.07; and √3.07 = 1.75 m².