Body Surface Area Calculator
Instant results as you type.
Fill in the values — results appear instantly.
For education only — this is not medical advice. The figures are population averages: real energy use, appetite and rate of loss vary from person to person, and weight loss slows as you get lighter. If you are pregnant, managing diabetes, heart or joint conditions, or taking medication, talk to a doctor before changing your diet or activity.
Body surface area is the area of skin covering a person, worked out from height and weight, and it is used in medicine wherever body size matters more than body mass — chemotherapy dosing, burn assessment, cardiac output, kidney function. There is no single agreed formula, so this gives the three that clinicians actually use side by side: Mosteller, which is simple enough to do on paper, Du Bois, which has been the reference since 1916, and Haycock, which is often preferred for children. They disagree by a few percent, and seeing that disagreement is more useful than being handed one number as though it were exact.
How to use it
- Pick your units — kilograms and centimetres, or pounds with feet and inches.
- Enter height and weight.
- All three formulas are shown at once. Mosteller is the headline because it is the most widely used, not because it is the most correct.
Examples
- 70 kg at 175 cm: 1.84 m² by Mosteller, 1.85 by Du Bois
- A 20 kg child at 110 cm: about 0.78 m²
Frequently asked questions
- What is body surface area used for?
- Mainly for dosing drugs where the margin between an effective dose and a harmful one is narrow — chemotherapy above all — because surface area tracks metabolic rate and blood volume better than weight alone does. It is also used to express cardiac output as a cardiac index, to estimate the extent of burns, and to normalise kidney function measurements so that results are comparable between a large adult and a small child. Outside those settings it is rarely needed: for most everyday questions about body size, BMI or plain weight is the more useful number.
- Which formula should I use?
- Whichever your institution uses, and if you are not in one, Mosteller. It is the most widely adopted, it is simple enough to check by hand, and it agrees closely with the others across normal adult sizes. Du Bois is the historical reference and is still specified in some protocols, though it is known to underestimate at the extremes of size. Haycock was derived with children in the sample and is often preferred in paediatrics. The choice matters less than consistency: switching formula partway through a course of treatment is the thing to avoid.
- Why do the three formulas disagree?
- Because none of them measures anything — they are all regression equations fitted to a modest number of real surface-area measurements taken decades ago, using different samples and different methods. Du Bois used nine subjects in 1916. Later formulas used larger and more varied groups, which is why they diverge most at the extremes: very small children, very tall people, and high body weights, where the original samples had few or no examples. Across ordinary adult sizes the three agree to within a couple of percent, which is why the disagreement is worth seeing rather than hiding.
- Can I use this to work out a drug dose?
- No. Please do not use this, or any general-purpose calculator, to determine a dose. Dosing depends on the specific drug and protocol, on kidney and liver function, on prior treatment, on capping rules for large body sizes, and on clinical judgement about the individual patient — none of which a page like this knows anything about. It is offered as a general reference for people who already know why they want the number. If a dose depends on it, the calculation belongs with the clinician prescribing it.