What body surface area (BSA) is
Body surface area, or BSA, is the total area of a person’s skin, expressed in square metres (m²). Since measuring real skin is impractical, it is estimated from two things we can measure easily: height and weight.
BSA matters in medicine because it tracks the body’s metabolic size better than weight alone. It shows up when dosing certain drugs (chemotherapy is the classic case), when reporting cardiac index, and when normalising kidney function. An average adult sits around 1.7 m², the long-standing reference figure.
How to use the calculator
- Pick your units: centimetres and kilograms, or feet with inches and pounds.
- Enter your height.
- Enter your weight.
- You will instantly see your BSA from the Mosteller formula, with the Du Bois value below it for comparison.
Everything runs in your browser; we never send or store your data.
The Mosteller formula
The Mosteller formula (1987) is the most widely used because it is so simple:
BSA = √(height_cm × weight_kg ÷ 3600)
For comparison, the calculator also shows the Du Bois and Du Bois formula (1916), the oldest and still common approach:
BSA = 0.007184 × height_cm^0.725 × weight_kg^0.425
Both give very similar results for average-build adults; the gap widens mostly at the extremes of weight.
Worked example
Take a person who is 170 cm tall and weighs 70 kg. With Mosteller: multiply 170 × 70 = 11,900, divide by 3600 = 3.3056, then take the square root = 1.82 m². With Du Bois: 0.007184 × 170^0.725 × 70^0.425 = 1.81 m². The two differ by just 0.01 m², showing how closely the formulas agree for a typical adult.
Reference values (Mosteller)
Estimated body surface area for some common height and weight combinations:
| Height / weight | BSA Mosteller (m²) | BSA Du Bois (m²) |
|---|---|---|
| 150 cm / 50 kg | 1.44 | 1.43 |
| 160 cm / 60 kg | 1.63 | 1.62 |
| 170 cm / 70 kg | 1.82 | 1.81 |
| 180 cm / 80 kg | 2.00 | 2.00 |
| 190 cm / 90 kg | 2.18 | 2.18 |
Why BSA is used instead of weight alone
Many body processes — resting energy expenditure, blood volume, renal flow — scale better with surface area than with mass. Dosing some medicines “per m²” spreads the drug more evenly across people of different sizes than dosing “per kg”. It is not flawless: in people with obesity, BSA can overestimate the dose, which is why oncology sometimes caps or adjusts the value. That call always belongs to the medical team.
Frequently asked questions
Should I use Mosteller or Du Bois?
For most people it makes no difference: for average-build adults they differ by hundredths of a square metre. Mosteller is easier to work out by hand and has become the standard in many hospitals. Du Bois is the classic that still appears in older tables and studies. This calculator shows both so you can compare.
What is a normal body surface area?
For an average adult it is roughly 1.6 to 1.9 m². The historical reference value for an adult is 1.73 m², which you will mostly see when normalising kidney function. Newborns are near 0.25 m² and it grows with age.
Can I calculate my own drug dose with this?
No. BSA is only one factor; the actual dose depends on the drug, your kidney and liver function, other treatments and clinical judgement. This tool is informational and gives an estimate — it does not replace advice from a healthcare professional. Use the result to understand the concept, never to self-medicate.
Does it work for children?
The Mosteller and Du Bois formulas are used in paediatrics too, but interpreting them and any dose calculation in children is more delicate and must be done by a paediatrician. Here you get the estimated area, not a treatment plan.