How this calculator works
Body surface area (BSA) is an estimate of the total surface area of the body, calculated from height and weight rather than measured directly. It scales more consistently with metabolic rate and organ function than body weight alone, which is why it shows up throughout medicine — most notably in calculating doses for chemotherapy and a handful of other drugs, and in normalizing measurements like cardiac output or kidney function so they can be compared between people of different sizes.
This calculator reports BSA using the Mosteller formula, the version most widely used in modern clinical practice because it is simple to compute and matches the more complex Du Bois formula closely for most adult body sizes. The original 1916 Du Bois formula is shown alongside it for comparison. Any medical dosing decision based on BSA is made by a qualified clinician using validated clinical tools — this calculator is for general reference and estimation only.
The formulas
Mosteller (1987): BSA (m²) = √(height(cm) × weight(kg) ÷ 3600)Du Bois & Du Bois (1916): BSA (m²) = 0.007184 × height(cm)^0.725 × weight(kg)^0.425Both formulas take height in centimeters and weight in kilograms and return BSA in square meters. They typically agree within about 1-2% for adults of average build and diverge more at the extremes of height and weight.
Worked example: 180 cm, 80 kg
- Mosteller: multiply height by weight: 180 × 80 = 14,400.
- Divide by 3,600: 14,400 ÷ 3,600 = 4.
- Take the square root: √4 = 2.00 m².
- Du Bois gives a very close 1.996 m² for the same measurements.
Frequently asked questions
Which formula should I use, Mosteller or Du Bois?
Mosteller is simpler to calculate and is the version most commonly used in current clinical software and reference tools. Du Bois is the original and still widely cited formula from 1916. For most adult body sizes the two agree closely; this calculator shows both so you can compare.
What is BSA used for?
Clinically, BSA is used to dose medications such as chemotherapy agents where a flat per-kilogram dose would be less consistent across very different body sizes, and to index measurements like cardiac output or glomerular filtration rate to a standard body size for comparison between patients.
Is 1.73 m² a normal BSA?
1.73 m² is a commonly used reference body surface area in medicine — for example, kidney function (eGFR) results are often normalized 'per 1.73 m²' so results are comparable across patients of different sizes. It is a reference constant, not a target or a definition of 'normal' for any individual.
Can I use this to calculate my own medication dose?
No. Medication dosing based on BSA must be calculated and verified by a qualified clinician or pharmacist using validated tools, since dosing errors can be serious. This calculator is for general reference and education only.
If someone weighs twice as much as another person of the same height, is their BSA twice as large?
No. Both formulas take roughly the square root of weight rather than using it directly, so BSA grows more slowly than weight itself. Under the Mosteller formula, doubling weight alone (height unchanged) multiplies BSA by only about 1.41 (the square root of 2), not by 2 — part of why BSA, rather than raw weight, is used to compare metabolic measurements between people of different sizes.