Body Surface Area Calculator

BSA by Du Bois, Mosteller, Haycock and Boyd.

Calculate body surface area using the Mosteller, Du Bois, Haycock and Boyd formulas. BSA is used for chemotherapy dosing, cardiac index and burn assessment.

Written and maintained by Mohit PatelLast checked August 4, 2026How we build these

Units

Height

Weight

Dosing protocols specify which formula to use, and they disagree by a few percent. Follow your local protocol rather than picking the most convenient number.

Body surface area (Mosteller)

1.84 m²

Du Bois1.85 m²

Haycock1.85 m²

Boyd1.85 m²

Spread across formulas0.01 m²

How the Body Surface Area Calculator works

Body surface area scales with metabolic processes more closely than weight does, which is why it is the basis for chemotherapy dosing, cardiac index, and estimating burn extent. Several formulas exist and they disagree by a few percent, so clinical protocols usually specify which one to use.

Also known as: BSA calculator · Du Bois body surface area · Mosteller BSA formula

Why body surface area is calculated at all

Body surface area is used clinically because several physiological quantities scale with surface area rather than with weight: cardiac output, glomerular filtration rate, and the dosing of a number of drugs.

It is most familiar from chemotherapy dosing, where doses are conventionally expressed in milligrams per square metre. The rationale is that surface area correlates better than weight with metabolic rate and drug clearance for many agents.

That rationale has been questioned for decades and the practice persists, partly because the historical dose-finding data was gathered that way. For some drugs, flat or weight-based dosing performs at least as well.

The formulas

The Du Bois formula from 1916 is the oldest in common use: 0.007184 times height in centimetres to the power 0.725 times weight in kilograms to the power 0.425. It was derived from nine subjects, which is a remarkably small basis for something so widely used.

The Mosteller formula, published in 1987, is far simpler: the square root of height in centimetres times weight in kilograms, divided by 3600. It agrees closely with Du Bois across most of the normal range and is easier to compute at a bedside.

Haycock and Gehan-George are also used, particularly in paediatrics. The differences between formulas are typically within a few percent for adults of average build and can be larger at the extremes, particularly in obesity, where Du Bois tends to underestimate.

The typical values

An average adult man is around 1.9 square metres and an average adult woman around 1.6. A newborn is roughly 0.25, and a child of ten around 1.14.

The figure rises with both height and weight but not proportionally with either, which is why two people of the same weight and different heights have different surface areas.

For dose calculations most protocols cap the surface area used, commonly at 2.0 or 2.2 square metres, because the relationship between surface area and drug clearance does not hold well in very large patients and uncapped dosing risks toxicity.

Where it is applied besides drug dosing

Indexed cardiac output, cardiac index, divides cardiac output by body surface area so that measurements are comparable between people of different sizes.

Glomerular filtration rate is conventionally reported normalised to 1.73 square metres, which was the average adult surface area in an American population in the 1920s and has been retained as a convention ever since.

Burn assessment uses the percentage of total body surface area affected, which is estimated by rules of thumb such as the rule of nines rather than by these formulas, since what matters is the proportion rather than the absolute figure.

Its limits

All of these formulas are estimates derived from small populations and validated against direct measurements that were themselves difficult to make. The uncertainty is real and it is rarely stated when a figure is quoted to three decimal places.

They perform least well in obesity, in oedema, in amputees and in people with unusual body proportions, all of which are situations where accurate dosing matters most.

This calculator is a convenience for checking arithmetic rather than a clinical tool. Any dose calculation that will be administered to a patient belongs with the clinician responsible for it, working from their own protocol and their own checks.

Where to go next

The Body Surface Area question rarely arrives on its own. These are the ones that usually come with it:

BMI Calculator — Body mass index with category and healthy weight range.
Ideal Weight Calculator — Target weight from four clinical formulas plus BMI range.
Lean Body Mass Calculator — Everything you weigh that is not fat.
Calorie & BMR Calculator — Daily calorie needs for losing, holding, or gaining weight.

Sources

Mosteller, N Engl J Med 1987 (PubMed)

Not medical advice. This calculator gives a general estimate, not medical advice. It cannot account for your individual health, medical history, or medication. Talk to a qualified healthcare professional before acting on any result.

Frequently asked questions

What is the Mosteller formula?

BSA in m² = the square root of (height in cm × weight in kg ÷ 3600). It is the most widely used because it is simple enough to do on a calculator at the bedside and agrees closely with the older, more complex equations.

Which BSA formula should I use?

Follow whatever your local protocol specifies, the choice matters because doses are calculated from it. Mosteller is the most common default. Du Bois is the historic standard from 1916 and can underestimate in obesity. Haycock was derived with children included.

Why is chemotherapy dosed by body surface area?

The practice dates from early trials where BSA correlated better than weight with the doses animals tolerated. It remains standard, though it is well recognised as an imperfect proxy: it ignores body composition, organ function and genetics, and there is ongoing work on better dosing models.

What is a normal body surface area?

Roughly 1.7 m² for an average adult, with typical values around 1.6 m² for women and 1.9 m² for men. A newborn is about 0.25 m². The figure is only meaningful next to the dose or index it is being used for.