Body Surface Area Calculator
Estimate body surface area (BSA) from height and weight using the Mosteller, Du Bois, and Haycock formulas — the measure clinicians use to scale drug doses.
How to use this calculator
- 1Choose metric or imperial units.
- 2Enter your height and weight.
- 3Read the body surface area from the Mosteller formula, the clinical default.
- 4Compare the Du Bois and Haycock estimates to see the small spread between methods.
How it works
Body surface area
Mosteller: BSA = √(height_cm × weight_kg ÷ 3600) Du Bois: BSA = 0.007184 × height^0.725 × weight^0.425 Haycock: BSA = 0.024265 × height^0.3964 × weight^0.5378 height in cm, weight in kg, BSA in m²
Body surface area is the total area of the skin, and in medicine it is a more useful scaling measure than weight alone for many purposes. It cannot be measured directly on a living person, so it is estimated from height and weight using empirical formulas fitted to real measurements. The Du Bois formula, published in 1916, was the long-standing standard; the Mosteller formula, a simple square root, has since become the most widely used because it is easy to compute by hand and agrees closely with the others in the normal range. Haycock's formula was validated across a broad span of body sizes, including infants. All express BSA in square metres, with a typical adult falling between about 1.5 and 2.0 m².
Worked example
A person 175 cm tall weighing 70 kg has a Mosteller BSA of √(175 × 70 ÷ 3600) = √3.40 ≈ 1.85 m². The Du Bois and Haycock formulas give almost the same figure, around 1.85–1.88 m², which is why the simple Mosteller version is the one clinicians reach for.
Body Surface Area Calculator: the complete guide
Why medicine uses surface area, not weight
For a surprising number of physiological quantities, body surface area is a better yardstick than body weight. Metabolic rate, the volume of blood the heart pumps, kidney filtration, and heat loss all scale more closely with surface area than with mass, because they are governed by exchange across surfaces rather than by sheer bulk. Two people of the same weight but different heights present different surface areas, and their bodies behave accordingly.
The most important practical use is drug dosing, especially in chemotherapy. Many powerful drugs have a narrow margin between an effective dose and a toxic one, and dosing per square metre of surface area gives a more consistent blood concentration across different body sizes than dosing per kilogram. Cardiac output and other measures are likewise 'indexed' to surface area so that values can be compared fairly between a small and a large patient. This is why BSA appears constantly on hospital charts.
The formulas and why they differ
Because surface area cannot be measured on a living body without elaborate scanning, every clinical BSA figure is an estimate from a formula. These formulas were built by measuring the actual skin area of a modest number of volunteers — historically by wrapping them in paper or applying known techniques — and fitting an equation to height and weight. The Du Bois formula came from just nine subjects in 1916, yet proved durable enough to remain a standard for decades.
Later formulas like Mosteller and Haycock used larger and more varied samples, and Haycock in particular extended validity to children and infants, where the Du Bois equation is less accurate. In the normal adult range all the common formulas agree to within a few percent, so the choice rarely matters clinically; Mosteller wins on simplicity. At the extremes — very small children, very large adults — the formulas diverge more, and the estimate should be treated with appropriate caution.
What a BSA figure means for you
For most people, body surface area is a number they will only encounter in a medical setting, on a dosing calculation or a report indexed to it. A typical adult sits between roughly 1.5 and 2.0 square metres, with 1.7 m² often used as a reference value. Knowing your own figure is useful mainly for understanding a prescription or a test result that has been scaled to it, rather than as a health metric in its own right.
It is worth remembering what BSA is not. Unlike BMI or body-fat percentage, it says nothing about whether your weight is healthy — it simply describes your overall size as an area. A very muscular person and a heavier, less muscular person of the same height and weight would have the same BSA. Its purpose is scaling, not assessment. When you see it on a chart, read it as the denominator that makes a dose or a physiological rate fair across body sizes, not as a verdict on your health.
Frequently asked questions
What is body surface area used for?
Mainly in medicine, to scale things that track surface area better than weight — drug doses (especially chemotherapy), cardiac output, and kidney function are commonly indexed per square metre. Dosing by surface area gives more consistent effects across different body sizes than dosing by weight alone.
Which BSA formula is most accurate?
In the normal adult range the common formulas — Mosteller, Du Bois, Haycock — agree within a few percent, so it rarely matters. Mosteller is the clinical default because it is simplest. Haycock is preferred for children and infants, where Du Bois is less reliable.
What is a normal body surface area?
A typical adult has a BSA of roughly 1.5 to 2.0 square metres, with about 1.7 m² often used as a reference. It scales with both height and weight, so taller and heavier people have larger values. It is a measure of overall size, not of health.
Is BSA the same as a health measure like BMI?
No. BSA describes your total size as an area and says nothing about whether your weight is healthy — a muscular and a less-muscular person of the same height and weight share the same BSA. BMI and body-fat percentage assess body composition; BSA is used purely for scaling doses and rates.