Estimate body surface area from height and weight, choose your main formula, and compare common BSA results in m2 and ft2.
How to use our Body Surface Area Calculator
- Choose Input unit system, then enter either Height (cm) and Weight (kg) or Height (feet), Height (inches), and Weight (lb).
- Select Primary formula to decide which equation appears as your main Body surface area result.
- Click Calculate to see Body surface area in m2 and ft2, the Primary formula used, and the Formula comparison table.
- Sanity-check the result by making sure your height and weight were entered in the correct unit system and by seeing whether the other formulas are only slightly different from your primary result.
Definitions
Body surface area: An estimate of the total outside surface of the body, usually written as BSA.
Body surface area (m2): Your main BSA result in square meters.
Body surface area (ft2): The same BSA result converted to square feet.
Primary formula: The equation you choose for the first result card.
Primary formula used: The exact equation name used to calculate your main answer.
Formula comparison: A table showing what each formula gives and how far each one is from your selected primary result.
Typical adult reference note: A rough context note for adult-sized results, not a personal target or diagnosis.
Input warning: A caution message shown when values are unusual or when the estimate may need extra care in interpretation.
Common mistakes and quick fixes
Mistake: Entering Height (cm) and Weight (kg) while Input unit system is set to US.
Fix: Change Input unit system to Metric (cm, kg) or re-enter your values in Height (feet), Height (inches), and Weight (lb).
Mistake: Typing total height into Height (inches), such as 67, instead of splitting it between Height (feet) and Height (inches).
Fix: In US mode, put the whole feet in Height (feet) and only the remaining inches in Height (inches).
Mistake: Leaving Weight (kg), Weight (lb), Height (cm), Height (feet), or Height (inches) blank.
Fix: Fill in every required field for the active Input unit system before you calculate.
Mistake: Assuming Body surface area is an exact measurement.
Fix: Treat Body surface area as an estimate and use the Formula comparison output to see how much different equations change the result.
Mistake: Comparing your Body surface area in m2 to a chart that uses ft2, or the other way around.
Fix: Use both Body surface area outputs and match the unit shown in your textbook, chart, or note.
Mistake: Thinking a small difference in Primary formula used means one result is wrong.
Fix: Check the Formula comparison table. Small differences between formulas are normal for the same height and weight.
Limitations & Key Assumptions / Boundary Conditions
- BSA formulas estimate surface area from height and weight. They do not directly measure the body.
- Results depend on the selected formula. This calculator shows one primary result first and the others separately instead of averaging them.
- If Input unit system is US, Height (inches) should be 0 to less than 12, with the rest entered in Height (feet).
- Height and weight must be greater than 0. Invalid, blank, or non-numeric entries stop the calculation.
- Very small or very large body sizes can still produce a mathematical result, but some published equations may be less reliable for unusual body proportions or sizes.
- The Typical adult reference note is broad context only. It is not meant for children, body-composition assessment, or treatment decisions by itself.
- Real clinical use may combine BSA with age, diagnosis, medication rules, and local protocols, so a chart or clinician may use a specific formula rather than another one.
Methodology
How the calculator works
This calculator first converts all active inputs to centimeters and kilograms when needed, then applies the selected BSA equation. The main result is the selected Primary formula, and the comparison table shows the other formulas beside it.
Unit conversions
height_cm = (Height (feet) x 30.48) + (Height (inches) x 2.54)
weight_kg = Weight (lb) x 0.45359237
bsa_ft2 = bsa_m2 x 10.7639104167
If Metric is selected, the calculator uses Height (cm) and Weight (kg) directly. If US is selected, it ignores the metric fields and uses only Height (feet), Height (inches), and Weight (lb).
BSA formulas used
Mosteller: BSA = sqrt((height_cm x weight_kg) / 3600)
Du Bois: BSA = 0.007184 x weight_kg^0.425 x height_cm^0.725
Haycock: BSA = 0.024265 x weight_kg^0.5378 x height_cm^0.3964
Gehan and George: BSA = 0.0235 x weight_kg^0.51456 x height_cm^0.42246
Fujimoto: BSA = 0.008883 x weight_kg^0.444 x height_cm^0.663
Boyd: BSA = 0.0003207 x height_cm^0.3 x weight_g^(0.7285 - 0.0188 x log10(weight_g))
weight_g = 1000 x weight_kg
Comparison math
For each formula in the table, the calculator shows its BSA in m2 and ft2, then compares it with your selected primary result.
absolute_difference = formula_bsa_m2 - primary_bsa_m2
percent_difference = (absolute_difference / primary_bsa_m2) x 100
A positive difference means that formula gives a larger estimate than your primary formula. A negative difference means it gives a smaller estimate.
Mini example
Using Height (cm) = 170 and Weight (kg) = 70 with Mosteller selected:
BSA = sqrt((170 x 70) / 3600) = sqrt(3.305555...) = 1.8181 m2
BSA in ft2 = 1.8181 x 10.7639104167 = 19.5701 ft2
If another formula gave 1.8097 m2, then its difference from the primary result would be about -0.0084 m2, or about -0.46%.
Interpretation notes
Most users should focus first on the main Body surface area result and the Primary formula used. The comparison table is there to show whether the formula choice changes the estimate only a little or by a more noticeable amount for the same person.
Assumptions used in this calculator
The calculator assumes height and weight are entered correctly for the active unit system, inches in US mode are less than 12, and all formulas are applied exactly as published. It does not adjust for body composition, limb loss, edema, pregnancy, or other factors that can matter in real-world medical settings.