This BSA calculator estimates body surface area in square meters (m²) from height and weight. It calculates BSA with the five formulas used in clinical practice: Mosteller, Du Bois, Haycock, Gehan-George and Boyd. You can compare the results side by side, in metric or imperial units.
The quickest formula to use by hand is Mosteller: BSA (m²) = √(height cm × weight kg / 3600). The oldest and most widely cited one is Du Bois: BSA (m²) = 0.007184 × weight0.425 × height0.725.
Body Surface Area Calculator
Medical disclaimer: This calculator is for educational and reference purposes only. Drug doses based on BSA must be determined and checked by a qualified healthcare professional according to the relevant protocol.
What Is Body Surface Area (BSA)?
Body surface area is the total area of the outer surface of the human body, expressed in square meters (m²). It is hard to measure directly, so in practice it is estimated from height and weight using one of the formulas below.
BSA is used in medicine instead of body weight alone because many physiological measures, such as metabolic rate, cardiac output and kidney function, scale more closely with body surface area than with weight.
BSA Formulas
In every formula below, W is weight in kilograms and H is height in centimeters. The result is in m².
| Formula | Equation | Notes |
|---|---|---|
| Mosteller (1987) | √(H × W / 3600) | Simplest to calculate by hand. Widely used in oncology and in many hospital systems. |
| Du Bois & Du Bois (1916) | 0.007184 × W0.425 × H0.725 | The original and most cited formula. Derived from measurements of only 9 people. |
| Haycock (1978) | 0.024265 × W0.5378 × H0.3964 | Validated in infants, children and adults. Often preferred in pediatrics. |
| Gehan & George (1970) | 0.0235 × W0.51456 × H0.42246 | Derived from a larger data set. Used in some oncology settings. |
| Boyd (1935) | 0.0003207 × H0.3 × Wg(0.7285 − 0.0188 × log10Wg) | Weight is in grams (Wg). Based on a broad range of body sizes, including children. |
Mosteller in imperial units: BSA (m²) = √(height in inches × weight in pounds / 3131).
Du Bois vs Mosteller: are they the same formula?
No. They are two separate formulas. Du Bois and Du Bois published their equation in 1916. Mosteller published a simplified square-root formula in 1987 so BSA could be calculated quickly on a pocket calculator. For people of average build the two give almost the same result. For people with obesity they can differ by several percent, as the examples below show.
Worked Examples
| Person | Mosteller | Du Bois | Haycock | Gehan-George | Boyd |
|---|---|---|---|---|---|
| Adult, 70 kg, 175 cm | 1.84 | 1.85 | 1.85 | 1.85 | 1.85 |
| Adult, 90 kg, 165 cm | 2.03 | 1.97 | 2.07 | 2.06 | 2.09 |
| Child, 20 kg, 110 cm | 0.78 | 0.78 | 0.78 | 0.80 | 0.80 |
Mosteller by hand (70 kg, 175 cm): 175 × 70 = 12,250 → 12,250 ÷ 3,600 = 3.403 → √3.403 = 1.84 m².
Du Bois by hand (70 kg, 175 cm): 700.425 ≈ 6.08 and 1750.725 ≈ 42.3 → 0.007184 × 6.08 × 42.3 = 1.85 m².
Which BSA Formula Should You Use?
- Follow your local protocol. Hospitals, cancer centers and clinical trials usually specify one formula, and doses should be calculated with that formula.
- Mosteller is the most common default because it is simple and agrees closely with Du Bois for most adults.
- Haycock or Mosteller are commonly used for children. Du Bois was derived from adults only.
- For severe obesity, amputation or extreme body types, all formulas become less accurate. Compare the results in the table above and discuss with the clinical team.
Normal BSA Values
- 1.73 m² is the standard reference BSA. Kidney function results such as eGFR are reported “per 1.73 m²” (mL/min/1.73 m²) so that people of different sizes can be compared.
- Adult men average roughly 1.9 m² and adult women roughly 1.6–1.7 m², depending on the population.
- Newborns are around 0.2–0.25 m². A typical 10-year-old is around 1.1 m².
There is no “ideal” BSA. It simply reflects body size and is not a health score like BMI.
What Is BSA Used For?
- Chemotherapy and other drug dosing: many cancer drugs are prescribed in mg/m². The dose is calculated as
dose (mg) = prescribed dose (mg/m²) × BSA (m²). For example, 100 mg/m² × 1.84 m² = 184 mg. - Kidney function: creatinine clearance and eGFR are normalized to 1.73 m² of BSA.
- Heart function: the cardiac index is cardiac output divided by BSA (L/min/m²).
- Pediatrics: some drug doses and fluid requirements for children are calculated per m².
Note: Burns are assessed with %TBSA (the percentage of total body surface area that is burned, using the Rule of Nines or a Lund-Browder chart). This is a different measurement from the BSA in m² calculated here.
Frequently Asked Questions
What is the formula for body surface area?
The most common is the Mosteller formula: BSA = √(height cm × weight kg / 3600). The Du Bois formula, BSA = 0.007184 × weight0.425 × height0.725, is the oldest and most cited.
How do I calculate BSA without a calculator app?
Use Mosteller: multiply height (cm) by weight (kg), divide by 3600, then take the square root. For 170 cm and 65 kg: 170 × 65 = 11,050 → ÷ 3600 = 3.07 → √3.07 = 1.75 m².
Which BSA formula is most accurate?
No formula is clearly best for everyone. For average adults, Mosteller, Du Bois, Haycock, Gehan-George and Boyd agree within a few percent. The differences grow for children and for people with obesity. Use the formula your institution or protocol specifies.
Can I use this BSA calculator for children?
Yes. The Mosteller, Haycock and Boyd formulas include children in their data and are commonly used in pediatrics. Always confirm pediatric doses with a clinician.
What does 1.73 m² mean on my kidney test?
It means your eGFR has been adjusted to a standard body size of 1.73 m², so it can be compared with reference ranges regardless of your actual size.
Related Calculators
- BMI Calculator: body mass index from height and weight.
- Ideal Weight Calculator: Devine, Robinson, Miller and Hamwi formulas.
- Lean Body Mass Calculator: estimate fat-free mass.
- BMR Calculator: basal metabolic rate.
References
- Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098. PubMed
- Du Bois D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med. 1916;17:863–871.
- Haycock GB, Schwartz GJ, Wisotsky DH. Geometric method for measuring body surface area: a height-weight formula validated in infants, children, and adults. J Pediatr. 1978;93(1):62–66.
- Gehan EA, George SL. Estimation of human body surface area from height and weight. Cancer Chemother Rep. 1970;54(4):225–235.
- Boyd E. The Growth of the Surface Area of the Human Body. University of Minnesota Press; 1935.