Body Surface Area (BSA) Calculator

Estimate the total surface area of the human body from height and weight, across the eight formulas clinicians actually use — and see how much they disagree.

Person	m²	ft²
Newborn child	0.25	2.69
Two-year-old child	0.50	5.38
Ten-year-old child	1.14	12.27
Adult female	1.60	17.22
Adult male	1.90	20.45

Written by the CalculatorBoss Health & Fitness Team · Every formula reproduced from its original publication and checked numerically · Last updated Aug 2026

What body surface area is

Body surface area is the total area of the outside of a human body, measured in square meters. An average adult sits somewhere near 1.7 m², roughly the area of a small dining table.

Measuring it directly is close to impossible outside a laboratory — the historical methods involved wrapping subjects in paper or coating them in plaster and then measuring the mold. So it is estimated instead, from the two numbers every clinic already has: height and weight. Every formula on this page is a curve fitted to a set of those laborious direct measurements, which is why they are named after the researchers who did the measuring.

Why medicine uses it instead of weight

Weight scales with volume; surface area does not. Double a person’s mass and their surface area rises by far less than double, because area grows with the square of length while volume grows with the cube. Metabolic processes track surface area more closely than mass, which makes it the better yardstick whenever the question is how much of something a body needs or can handle.

That is why it turns up in cardiac index, where cardiac output is divided by body surface area so a small patient and a large one can be compared on the same scale, in renal clearance measurements, in burn assessment, and most visibly in chemotherapy dosing, where doses are prescribed in milligrams per square meter.

It is also a reasonable proxy for fat-free mass — bone, muscle, organs, blood, everything that is metabolically active — in a way body weight alone is not, since weight cannot distinguish muscle from fat.

The eight formulas, in full

All eight take weight in kilograms and height in centimeters and return square meters. The calculator converts your input before applying them.

Du Bois         BSA = 0.007184 × W^0.425 × H^0.725
Mosteller       BSA = 0.016667 × W^0.5 × H^0.5
Haycock         BSA = 0.024265 × W^0.5378 × H^0.3964
Gehan & George BSA = 0.0235 × W^0.51456 × H^0.42246
Boyd            BSA = 0.0333 × W^{(0.6157 − 0.0188 log₁₀W)} × H^0.3
Fujimoto        BSA = 0.008883 × W^0.444 × H^0.663
Takahira        BSA = 0.007241 × W^0.425 × H^0.725
Schlich (women) BSA = 0.000975482 × W^0.46 × H^1.08
Schlich (men)   BSA = 0.000579479 × W^0.38 × H^1.24

Two things stand out. Boyd is the only one whose weight exponent is not fixed — it shrinks as weight rises, which is an attempt to handle very large and very small bodies with one curve. Schlich is the only one that splits by sex, and it leans much harder on height than any of the others, with an exponent above 1.

Takahira is Du Bois with a different constant. Fujimoto and Takahira were both fitted on Japanese populations, which is why they sit at opposite ends of the range for a tall Western frame.

Worked through with the numbers the form opens on — a 162-pound man of 5′10″, which is 73.48 kg and 177.8 cm — Du Bois gives 0.007184 × 73.48^0.425 × 177.8^0.725, or about 1.91 m².

Which formula to use

Mosteller is the practical default. It is the simplest — the square root of height times weight divided by 3600 — it can be done on any calculator, and it agrees closely with Du Bois across the normal adult range. Most hospital protocols specify it for that reason.

Du Bois is the historical standard, published in 1916 from just nine subjects, and still the reference most papers compare against. It is known to underestimate in obese patients.

Haycock and Gehan & George were both fitted with children included, so they behave better at small body sizes than Du Bois does.

The right answer in a clinical setting is whichever one the local protocol names, because consistency matters more than picking the theoretically best curve. If you are checking a dose someone else calculated, use the same formula they did.

How much they disagree, and when it matters

For an average adult the eight results usually fall within about 5% of each other, and the chart above shows the spread for whatever you entered. That sounds small until you remember what the number is used for: a 5% swing on a chemotherapy dose is a real difference in both effect and toxicity.

The spread widens at the extremes. Very tall, very short, very heavy and very light bodies all sit outside the ranges these curves were fitted on, and the formulas diverge most exactly where confidence should be lowest. Schlich in particular, with its height exponent above 1, pulls away from the others for unusually tall people.

The argument about chemotherapy dosing

Dosing cytotoxic drugs per square meter has been standard since the 1950s, and it is genuinely contested. The case against is that body surface area was adopted partly for convenience — it let animal doses be scaled to humans — and that it correlates poorly with the things that actually determine how a drug behaves, such as liver enzyme activity and renal clearance. For drugs with a narrow therapeutic index, where the gap between an effective dose and a toxic one is small, an imprecise scaling factor is a real hazard.

The case for is more practical: dosing by surface area still produces less variation in exposure than dosing by weight alone, and decades of trial data are expressed in those units. Some drugs have since moved to flat dosing or to targets based on measured clearance, but per-square-meter dosing remains widespread, and this calculator is not a substitute for a pharmacist’s calculation.

Where the estimate breaks down

It is a curve fit, not a measurement. Du Bois was built on nine people. Even the larger studies used tens to low hundreds of subjects.
Body shape is invisible to it. Two people of identical height and weight with different builds get identical results and do not have identical surface areas.
Accuracy falls at the extremes of height and weight, and for very obese patients some clinicians prefer body mass index or an adjusted weight instead.
Amputation, edema and pregnancy all break the assumptions, and none of the formulas account for them.
It says nothing about composition. A high surface area does not mean high muscle mass or good health.

Frequently asked questions

What is a normal body surface area?

Around 1.9 m² for an average adult man and about 1.6 m² for an average adult woman. A newborn is near 0.25 m² and a ten-year-old around 1.14 m².

Which body surface area formula is most accurate?

No single one is best for everybody. Mosteller is the usual clinical default because it is simple and agrees well with Du Bois across normal adult sizes; Haycock and Gehan & George behave better in children. In practice, use whichever your local protocol specifies.

How do you calculate BSA with the Mosteller formula?

Take height in centimeters times weight in kilograms, divide by 3600, and take the square root. For 177.8 cm and 73.48 kg that is the square root of 3.629, or about 1.90 m².

Why do the formulas give different answers?

Each was fitted to a different set of directly measured people, in different decades and different populations. Fujimoto and Takahira were built on Japanese subjects, Du Bois on nine Americans in 1916. Different data produces different curves.

Does body surface area depend on gender?

Only in the Schlich formula, which has separate equations for men and women. The other seven use height and weight alone, so a man and a woman of the same size get the same answer.

Why is chemotherapy dosed by body surface area?

Because drug handling tracks metabolic size better than it tracks weight, and surface area is a closer proxy for metabolic size. It is an imperfect standard and is actively debated, but decades of trial data are expressed in milligrams per square meter.

Is BSA the same thing as BMI?

No. Body surface area estimates how much outside surface a body has, in square meters. Body mass index is weight divided by height squared and is used to classify weight status. They answer different questions from the same two inputs.

How is body surface area actually measured?

Historically by coating or wrapping subjects and measuring the covering, and more recently with three-dimensional body scanning, which is how the Schlich equations were derived. Both are research procedures rather than anything done in a clinic.

This calculator is provided for general education and is not medical advice. Body surface area estimates must not be used to calculate or check medication doses; drug dosing is carried out by qualified clinicians and pharmacists using the formula and the patient data their protocol specifies. If you have a question about a dose or a treatment, speak to the prescribing team. Learn more about how we build these tools or read our privacy policy.