BSA Calculator (Body Surface Area)
A person who is 180 cm tall and weighs 75 kg has a body surface area of about 1.94 m² by the Mosteller formula. This BSA calculator turns your height and weight into your total body surface area in square meters, the single number clinicians reach for when they need a size measure that tracks the whole body rather than one dimension. It runs the Mosteller formula for your primary result because that method is the most widely used bedside estimate, and it also reports the older Du Bois and Du Bois value so you can compare the two side by side. You can work in metric units, entering height in centimeters and weight in kilograms, or switch to US units and enter height in inches and weight in pounds. The tool converts your US figures to centimeters and kilograms behind the scenes, then shows the exact height and weight it used so nothing about the calculation is hidden. Body surface area is used to scale doses, index cardiac output, and describe burn coverage, which is why a reliable estimate matters more than a rough guess based on weight alone.
Quick answer
Body surface area, or BSA, is the total external area of the body measured in square meters, and it grows with both height and weight.
What this tells you
- •Body surface area, or BSA, is the total external area of the body measured in square meters, and it grows with both height and weight.
- •The Mosteller formula, BSA = sqrt((height in cm × weight in kg) / 3600), is the primary estimate here because it is simple and accurate across most body sizes.
- •The Du Bois formula, 0.007184 × height^0.725 × weight^0.425, is the classic 1916 method and usually lands within a few percent of the Mosteller result.
- •A typical adult BSA falls between roughly 1.5 and 2.0 m², while children and infants have much smaller values.
- •BSA is often preferred over weight alone for scaling drug doses because it correlates more closely with metabolic rate and organ size.
- •This tool is informational only and does not replace a dosing calculation or judgment made by a qualified clinician.
How to Use
- 11. Choose your unit system. Select Metric to enter height in centimeters and weight in kilograms, or US to enter height in inches and weight in pounds.
- 22. Enter your height in the height field using the unit shown for the mode you picked.
- 33. Enter your weight in the weight field, again matching the selected unit system.
- 44. Press Calculate to see your Mosteller BSA as the primary result, with the Du Bois BSA listed underneath for comparison.
- 55. Check the height and weight the tool reports back in centimeters and kilograms to confirm any unit conversion matched what you intended.
How It Works
Formula
Mosteller: BSA = sqrt((height_cm × weight_kg) / 3600). Du Bois: BSA = 0.007184 × height_cm^0.725 × weight_kg^0.425The Mosteller formula multiplies height in centimeters by weight in kilograms, divides by 3600, and takes the square root, giving body surface area in square meters. It was published in 1987 as a shortcut that could be done on a basic calculator, and it has become the default in most clinical settings because it is accurate and easy to check. The Du Bois formula, published in 1916, raises height and weight to fixed exponents and multiplies by a constant. It was derived from direct measurements on a small number of people, so it can slightly underestimate BSA at the extremes of body size, but for most adults the two formulas agree closely. When you enter US units, height in inches is multiplied by 2.54 to get centimeters and weight in pounds is divided by 2.2046 to get kilograms before either formula runs. Both results are rounded to two decimal places for display.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Average adult in metric units
Multiplying 180 cm by 75 kg gives 13500, dividing by 3600 gives 3.75, and the square root of 3.75 is about 1.94 m². The Du Bois formula lands on the same 1.94 m² here, showing how closely the two methods agree for a typical adult.
Adult entered in US units
70 inches converts to 177.8 cm and 160 pounds converts to about 72.6 kg. Feeding those into the Mosteller formula gives sqrt((177.8 × 72.6) / 3600), which works out to roughly 1.95 m². The tool shows the converted 177.8 cm and 72.6 kg so you can confirm the conversion.
Smaller adult
165 cm times 60 kg is 9900, divided by 3600 is 2.75, and the square root of 2.75 is about 1.66 m². This falls at the lower end of the usual adult range, which is roughly 1.5 to 2.0 m².
A young child
For a child of 100 cm and 16 kg, 100 times 16 is 1600, divided by 3600 is 0.4444, and the square root is about 0.67 m². Children have much smaller body surface areas than adults, which is exactly why BSA rather than weight alone is used to scale many pediatric doses.
Typical Body Surface Area Values
Approximate Mosteller BSA for a range of common height and weight pairings in metric units.
| Height (cm) | Weight (kg) | Mosteller BSA (m²) | Group |
|---|---|---|---|
| 100 | 16 | 0.67 | Young child |
| 140 | 35 | 1.17 | Older child |
| 165 | 60 | 1.66 | Smaller adult |
| 175 | 70 | 1.84 | Average adult |
| 180 | 75 | 1.94 | Average adult |
| 190 | 100 | 2.30 | Larger adult |
These figures are rounded estimates for illustration and will vary with body composition and the exact formula used.
Why body surface area is used instead of weight
Body surface area gives a single measure that reflects both how tall and how heavy a person is, which makes it a better proxy for metabolic size than weight on its own. Two people can share the same weight but have very different heights, and their bodies process many substances at rates that track surface area more closely than mass. That is why BSA has been the standard scaling factor in areas like chemotherapy dosing for decades.
The Mosteller formula became popular because it is easy to compute and hard to get wrong. Before it appeared in 1987, clinicians often relied on printed nomograms or the more complex Du Bois equation. Mosteller reduced the whole calculation to a single square root that anyone could do quickly, and studies since then have shown it matches the older methods well across a wide range of body sizes.
BSA also underpins indexed measurements. Cardiac output is often reported as the cardiac index, which is cardiac output divided by BSA, so that values can be compared fairly between a small and a large person. Kidney function estimates and some blood volume calculations are indexed the same way. In each case, dividing by surface area removes the effect of raw body size and leaves a number that means the same thing across different people.
Common mistakes
- Entering height in the wrong unit, such as typing inches while the tool is set to metric. Always match the unit shown in the field to the number you enter.
- Mixing units within one calculation, like height in centimeters and weight in pounds. Pick one unit system and use it for both fields.
- Assuming the Mosteller and Du Bois values must be identical. They use different math and will often differ by a small amount, which is normal.
- Treating a BSA figure as a dosing instruction. This tool estimates surface area only and does not calculate any medication dose.
- Confusing body surface area in square meters with body mass index. BMI is weight over height squared and is a different measure with different units.
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