Body surface area (BSA) is the total area of the outside of the body, measured in square meters. It is used in medicine to scale drug doses, especially for chemotherapy, and to index measurements such as cardiac output and kidney function to body size. Since nobody measures skin directly, BSA is estimated from height and weight, and this calculator shows the five most common formulas together.
How to use the body surface area calculator
- Choose US or metric units.
- Enter height and weight. The calculator accepts infant to adult sizes.
- Pick the main formula to highlight; the others appear below it with the full comparison table.
- Read the result in square meters, with square feet as a secondary unit.
Body surface area formulas
With weight W in kilograms and height H in centimeters:
Mosteller’s version is a simplification of Gehan and George’s work that can be done on a basic calculator, which is a large part of its popularity.
Worked example
An adult who is 170 cm tall and weighs 70 kg:
Mosteller: √(170 × 70 ÷ 3600) = √3.306 = 1.82 m²
Du Bois: 0.007184 × 700.425 × 1700.725 ≈ 1.81 m²
Haycock, Gehan–George and Boyd all give about 1.83 m², so the five formulas span just 0.02 m².
Where the formulas differ
For average adults the results land within 1–3% of each other, which is smaller than the uncertainty in most measured heights and weights. Differences grow at the extremes:
- Infants and small children: Du Bois was derived from measurements of just nine people and is often reported to underestimate BSA in infants. Haycock and Gehan–George, fitted to data that included children, handle small bodies better.
- Severe obesity: formulas diverge by 5% or more because body shape departs from the proportions in the original studies. Some oncology protocols cap BSA at a set value for this reason.
- Amputation or very unusual proportions: no height-and-weight formula can capture the real surface area.
Typical BSA values
| Person | Height | Weight | BSA (Mosteller) |
|---|---|---|---|
| Newborn | 50 cm | 3.5 kg | about 0.22 m² |
| Young child | 110 cm | 18 kg | about 0.74 m² |
| Adult woman | 162 cm | 70 kg | about 1.77 m² |
| Adult man | 175 cm | 88 kg | about 2.07 m² |
The reference value of 1.73 m², used to standardize kidney function (eGFR), dates from a 1928 study of adult kidney function and reflected the average adult of that era; many adults today are larger.
Related measurements
BSA tells you about body size, not composition. The BMI calculator compares weight with height, and the lean body mass calculator estimates how much of that weight is non-fat tissue. To convert measurements before entering them, use the height converter or the kilograms to pounds converter.
Informational only — not medical advice. Never use this page to calculate a medication dose; BSA-based doses must be calculated and verified by the prescribing clinician or pharmacist.
Frequently asked questions
What is a normal body surface area?
For adults, BSA is usually between about 1.5 and 2.2 square meters. A value of 1.73 m² is the standard reference used to normalize kidney function, and averages are roughly 1.9 m² for men and 1.6 m² for women.
Which BSA formula is most accurate?
For adults of average build the formulas agree within a few percent. Mosteller is the most widely used because it is simple and performs well; Haycock and Gehan–George were fitted to data that included children and are often preferred in pediatrics.
Why is BSA used instead of weight for some drug doses?
Many physiological processes, including metabolic rate, cardiac output and kidney filtration, scale more closely with surface area than with weight. That makes BSA a common basis for chemotherapy doses and for indexing heart and kidney measurements.
Does this calculator work for children?
Yes. It accepts heights from about 30 cm and weights from 0.5 kg. For pediatric dosing, clinicians typically use Mosteller or Haycock and confirm results with institutional protocols.