Body surface area

Your body surface area in square metres. Doctors use it for some medicine doses.

Your details

Your body surface area (Mosteller)

1.84 m²

Square metres of skin, roughly

Du Bois formula1.83 m²
Haycock formula1.85 m²
Typical adultabout 1.7 to 2.0 m²
Compared with the 1.73 m² standard6% larger
eGFRadd a result from a blood test to see it without the 1.73 m² scaling

Doctors use body surface area to work out some medicine doses, such as chemotherapy. Your care team will always do their own sums, so use this to understand the number, not to change a dose.

The working

Mosteller, the simple one

In 1987 Raymond Mosteller showed that a square root does the job almost as well as the older formulas:

BSA = √(cm × kg ÷ 3600)

At 11 st 4 lb (71.7 kg) and 5 ft 7 in (170.2 cm): 170.2 × 71.7 = 12,196, divided by 3,600 is 3.39, and the square root is 1.84 m². About the size of a single duvet.

A bit of history

Measured with paper and plaster

In 1916 Delafield and Eugene Du Bois worked out their formula by covering nine people in paper moulds and measuring the pieces. One of the nine was a child. It is still used today, more than a century later.

Where it is used

In hospital

Chemotherapy doses are often set per square metre.
Heart output is sometimes compared using the cardiac index, which divides by BSA.
Burns are assessed as a percentage of body surface.

Kidney results and BSA

Why 1.73 m² keeps turning up

Kidney blood test results (eGFR) are scaled to a standard body surface area of 1.73 m² so that people of different sizes can be compared. For medicine doses at the extremes of body size, the BNF describes taking that scaling off: absolute GFR equals eGFR times your BSA divided by 1.73. Add an eGFR and the page does this for you.

For someone of 120 kg and 170 cm, the Du Bois BSA is about 2.28 m², so an eGFR of 60 is roughly 79 ml/min in absolute terms. Pharmacists may also use creatinine clearance instead. This is to help you follow the conversation, not to change any dose.

Pick the formula your clinic uses. Mosteller is the simplest and widely used, Du Bois is the oldest, and Haycock was checked in babies and children as well as adults.

Questions

Common questions

What is a normal body surface area?

About 1.6 to 1.9 m² for most women and 1.9 to 2.2 m² for most men.

Which BSA formula is most accurate?

For adults, Mosteller and Du Bois agree to within a few percent. Haycock is often preferred for children.

Can I use this to check a chemotherapy dose?

Use it to understand the number, but never to change a dose. Your oncology team calculates and double checks every dose.

Sources

Last checked 21 October 2026. Spotted something wrong? Tell us and we will fix it.

About medicine doses

If you have a question about a dose worked out from your size, ask your pharmacist, nurse or doctor. They will be glad you asked. For urgent worries, call NHS 111.