Calculate your body surface area in square metres from your weight and height, compare the four standard formulas side by side and see how far apart they are.
The headline result above uses the formula you select here. All four are still compared in the table and chart below.
| Formula | BSA | How it is built |
|---|
Each bar length is proportional to that formula's body surface area. Close bars mean the formulas agree; a long gap means the choice of formula matters for your numbers.
For beginners: how to read this result
Describe the task to the AI assistant and continue from the result.
Open AI assistant →To get a result, load a preset or enter your own values: body weight and height. Use the unit toggle to switch between metric (kg and cm) and imperial (lb and in), then pick the formula button you want for the headline number. All four formulas are still calculated and compared below.
What body surface area is
Body surface area, or BSA, is the total external area of the skin covering the body, expressed in square metres. It scales with both weight and height, so two people with the same weight but different heights have different surface areas. A typical adult sits roughly between 1.5 and 2.0 m², while a young child is well under 1.0 m².
How the four formulas work
BSA cannot be measured directly in everyday practice, so it is estimated from weight and height using formulas fitted to real measurements. This calculator includes the four most common ones, with W as weight in kilograms and H as height in centimetres.
- Mosteller: BSA equals the square root of W times H divided by 3600. It is the simplest and the most widely used, which is why it is the default headline formula here.
- Du Bois: BSA equals 0.007184 times W to the power 0.425 times H to the power 0.725. One of the oldest formulas, still common in clinical references.
- Haycock: BSA equals 0.024265 times W to the power 0.5378 times H to the power 0.3964. Fitted on a sample that included infants and children.
- Gehan and George: BSA equals 0.0235 times W to the power 0.51456 times H to the power 0.42246. Also derived from a wide age range.
Reading the comparison and the spread
The comparison table shows the BSA from every formula for the same inputs, and the spread tells you the gap between the lowest and the highest result. The visual chart draws one bar per formula, with bar length proportional to that formula’s surface area, so you can see at a glance whether the formulas agree or diverge. A small spread is normal; when it is wider, the choice of formula matters and you should note which one a given number came from.
What is not included
This tool estimates total body surface area only. It does not calculate drug doses, body mass index, ideal weight or the surface area of individual body regions, and it does not account for body composition, amputations or unusual body shapes. Body surface area is used in clinical settings such as chemotherapy and drug dosing; this calculator is for general information and any medical or dosing decision must be made by a qualified clinician.