How much skin does a body have? Body surface area in m2 and square feet from height and weight, by five formulas from Mosteller to Boyd, for adults and babies, with the spread between them.
Body Surface Area Calculator - Mosteller, Du Bois, BSA m2
How much skin does a body have? Body surface area in m2 and square feet from height and weight, by five formulas from Mosteller to Boyd, for adults and babies, with the spread between them.
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Body surface area from height and weight: the short version
A newborn of 3.5 kg carries about 630 cm² of skin for every kilogram of weight; an adult of 70 kg carries about 260 cm². Body surface area (BSA) does not grow in step with weight, and that is why medicine uses it to scale some doses and to normalize measurements between people of different sizes. This calculator works it out from height and weight in pounds and feet or in kilograms and centimeters, with the five formulas most often quoted: Mosteller, Du Bois, Haycock, Gehan and George, and Boyd. For a 70 kg adult of 170 cm all five land between 1.81 and 1.83 m².
Three entries and the five formulas
- Units - U.S. (pounds, feet and inches) or metric (kilograms, centimeters). The formulas themselves take kg and cm.
- Weight - from 4.4 to 661 lb (2 to 300 kg), so babies are covered as well as adults. Decimals are fine.
- Height - feet plus inches, or centimeters, from 45 to 230 cm. For a baby, the measured length lying down.
- Read the result - BSA by Mosteller in m² and square feet, the range of all five formulas, each one on its own row with its difference from Mosteller, and a note when they disagree by 10% or more.
What the formulas have in common, and where they part
Measuring skin directly is slow, so every formula here is a curve fitted to people whose surface was measured, and each one takes only weight and height. Mosteller is the simplest: the square root of height times weight divided by 3600. Du Bois, Haycock and Gehan and George raise weight and height to fixed powers and multiply them; Boyd lets the power on weight shrink slightly as weight rises. For an adult of ordinary build the five agree within about 1 to 3%, because that is the kind of body most of them were fitted on.
They part at the edges. In the comparison of 25 formulas by Redlarski and colleagues in Scientific Reports, the largest gaps appeared for children and for short or heavy adults, and between Du Bois and Haycock alone the difference reached 0.82 m² at high weights. A validation against 3D body scans of 1,435 adults by Kuehnapfel and colleagues found that some lesser-known formulas fitted best, which is a reminder that no single formula is "the" body surface area.
The five, written out with W in kilograms and H in centimeters, as tabulated by Redlarski and colleagues (Mosteller in its square-root form):
| Formula | BSA in m² | Note |
|---|---|---|
| Mosteller | square root of (H × W / 3600) | the simplest; a square root |
| Du Bois | 0.007184 × W0.425 × H0.725 | the oldest of the five |
| Haycock | 0.024265 × W0.5378 × H0.3964 | fitted on infants, children and adults |
| Gehan and George | 0.0235 × W0.51456 × H0.42246 | powers close to Haycock |
| Boyd | 0.0003207 × (1000W)0.7285 - 0.0188 log10(1000W) × H0.3 | weight power falls as weight rises |
BSA for ten body sizes
Each row run through the calculator. The spread column is the highest of the five formulas minus the lowest, as a share of the lowest.
| Weight, height | Mosteller | Du Bois | Range of five | Spread |
|---|---|---|---|---|
| 3.5 kg, 50 cm | 0.220 | 0.209 | 0.21 to 0.23 | 12.1% |
| 10 kg, 75 cm | 0.456 | 0.437 | 0.44 to 0.48 | 9.9% |
| 20.6 kg, 115.5 cm | 0.813 | 0.813 | 0.81 to 0.83 | 2.2% |
| 40 kg, 150 cm | 1.291 | 1.303 | 1.29 to 1.30 | 1.3% |
| 60 kg, 165 cm | 1.658 | 1.659 | 1.66 to 1.67 | 0.8% |
| 70 kg, 170 cm | 1.818 | 1.810 | 1.81 to 1.83 | 1.4% |
| 81.6 kg, 177.8 cm | 2.008 | 1.995 | 2.00 to 2.02 | 1.3% |
| 90 kg, 193 cm | 2.197 | 2.208 | 2.19 to 2.21 | 1.0% |
| 100 kg, 180 cm | 2.236 | 2.195 | 2.20 to 2.27 | 3.2% |
| 136.1 kg, 162.6 cm | 2.479 | 2.324 | 2.32 to 2.59 | 11.6% |
Four things the BSA numbers show
Who looks up a body surface area
Nursing and pharmacy students checking a homework BSA by hand against all five formulas. Parents curious about the number written on a child's chart. Patients who saw "m²" next to a lab result or a treatment plan and want to know what it means for their own size. Anyone comparing formulas who wants to see how far apart they really are for one body. What none of them should do is turn the number into a dose: that is the prescriber's job, with a formula chosen by protocol and a weight and height measured on the day.
BSA questions, answered briefly
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