Calculate body surface area from weight and height in kg or lbs and cm or in, using the Mosteller formula, with results shown in m² and ft².
Medical note: This calculator provides an estimate only and is not medical advice. Do not use this result to adjust medication doses or make treatment decisions—clinical use of BSA (including dosing) should be determined by a licensed clinician, especially for children, pregnancy, kidney/liver disease, cancer treatment, or other medical conditions.
BSA Formula
The BSA calculator uses the Mosteller formula to estimate body surface area from height and weight. Weight is converted to kilograms and height is converted to centimeters before the formula is applied.
BSA = sqrt((W * H) / 3600)
- BSA = body surface area in square meters, m²
- W = weight in kilograms, kg
- H = height in centimeters, cm
- 3600 = Mosteller formula constant
If you enter weight in pounds, the calculator first converts pounds to kilograms:
W_kg = W_lb * 0.453592
If you enter height in inches, the calculator first converts inches to centimeters:
H_cm = H_in * 2.54
The calculator also converts the final BSA from square meters to square feet:
BSA_ft2 = BSA_m2 * 10.7639
- Basic BSA result: uses height and weight to calculate BSA in m² with the Mosteller formula.
- Unit conversion: accepts kg or lb for weight and cm or in for height, then converts to kg and cm for the formula.
- Square feet output: multiplies the m² result by 10.7639 to show BSA in ft².
Typical BSA Ranges
These are general reference ranges. BSA varies with body size, age, and body composition.
| Group | Typical BSA Range | Notes |
|---|---|---|
| Newborn | About 0.20 to 0.25 m² | Depends heavily on birth weight and length |
| Child | About 0.5 to 1.4 m² | Increases as height and weight increase |
| Adult | About 1.5 to 2.2 m² | Many average adults fall near 1.7 to 2.0 m² |
| Large adult | Above 2.2 m² | Can occur with greater height, weight, or both |
Common Unit Conversions for BSA Calculations
| Conversion | Formula | Example |
|---|---|---|
| Pounds to kilograms | lb × 0.453592 | 150 lb = 68.0388 kg |
| Inches to centimeters | in × 2.54 | 68 in = 172.72 cm |
| Square meters to square feet | m² × 10.7639 | 1.80 m² = 19.3750 ft² |
Example
Example 1: Calculate BSA for a person who weighs 70 kg and is 175 cm tall.
BSA = sqrt((70 * 175) / 3600)
BSA = sqrt(12250 / 3600) = 1.8447 m^2
Converted to square feet:
BSA_ft2 = 1.8447 * 10.7639 = 19.8560 ft^2
Example 2: Calculate BSA for a person who weighs 150 lb and is 68 in tall.
First convert the inputs:
W_kg = 150 * 0.453592 = 68.0388
H_cm = 68 * 2.54 = 172.72
Then apply the Mosteller formula:
BSA = sqrt((68.0388 * 172.72) / 3600) = 1.8067 m^2
Converted to square feet:
BSA_ft2 = 1.8067 * 10.7639 = 19.4475 ft^2
FAQ
What is BSA?
BSA means body surface area. It is an estimate of the total external surface area of the body. BSA is often used in medical and health-related calculations because it can better reflect body size than weight alone.
Which BSA formula does this calculator use?
It uses the Mosteller formula: BSA = square root of weight in kilograms times height in centimeters divided by 3600. This formula is commonly used because it is simple and gives results close to more complex BSA equations for many people.
Why are height and weight converted before calculating BSA?
The Mosteller formula used here requires weight in kilograms and height in centimeters. If you enter pounds or inches, those values must be converted first so the formula uses the correct units.
