Body Surface Area Calculator
Calculate body surface area (BSA) using the Mosteller formula — used in drug dosing and oncology.
How to use this tool
- Enter weight and height in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your body surface area and the full breakdown beneath it.
Body surface area (BSA) is used in drug dosing, especially chemotherapy. The Mosteller formula is BSA = √(height_cm × weight_kg ÷ 3600).
⚠ This tool is for general information and education only and is not medical advice. Consult a qualified healthcare professional before making health decisions.
Formula
BSA (m²) = √( height (cm) × weight (kg) ÷ 3600 )
This is the Mosteller formula.
How it works
Body surface area is estimated using the Mosteller formula, which takes the square root of the product of height in centimetres and weight in kilograms divided by 3600. The formula is widely used in clinical practice for drug dosing, particularly in oncology and renal medicine, because many physiological variables scale better with surface area than with weight alone. The Mosteller approximation typically agrees with more complex formulae to within 2–3% for adults of average proportions.
Worked example
- Weight = 70 kg, Height = 175 cm.
- Multiply: 175 × 70 = 12 250.
- Divide by 3600: 12 250 ÷ 3600 = 3.4028.
- Take the square root: √3.4028 ≈ 1.845, rounded to 1.84 m².
BSA = 1.84 m²
Common mistakes to avoid
- Entering weight in pounds instead of kilograms — the Mosteller formula uses kg; entering lbs produces a BSA roughly 47% too high.
- Using BSA from this estimate for actual drug dose calculation without clinical verification — BSA-based dosing requires confirmation by a pharmacist or physician.
- Confusing BSA (m squared) with BMI (kg/m squared) — these are entirely different metrics with different formulas and clinical uses.
Key terms
- Body surface area (BSA)
- The total skin surface of the human body, expressed in square metres, used to normalise drug doses and physiological measurements.
- Mosteller formula
- A simplified BSA formula (√(height × weight / 3600)) published in 1987, favoured for its ease of calculation.
- Oncology dosing
- The practice of calculating chemotherapy doses per unit of BSA (e.g. mg/m²) to account for differences in body size between patients.
- Normalisation
- Expressing a physiological measurement relative to body size so values can be compared between individuals of different stature.
- DuBois formula
- An earlier BSA formula (1916) that uses exponents of height and weight; the Mosteller formula is a simpler approximation of similar accuracy.
Frequently asked questions
- What is the Mosteller formula?
- BSA (m²) = √(height in cm × weight in kg ÷ 3600). It is simple and accurate enough for most clinical purposes.
- Why is BSA used for drug dosing?
- BSA correlates better with organ size and cardiac output than weight alone, making it the preferred scaling factor for chemotherapy and many IV medications.