Body Surface Area Calculator
Compare all 5 clinical BSA formulas simultaneously — Mosteller, DuBois, Haycock, Gehan & George, and Boyd.
Enter Your Measurements
ft
in
Mosteller BSA (most common)
—
m²
Average adult BSA ≈ 1.7 m²
All 5 Formula Results Compared
What is Body Surface Area?
Body Surface Area (BSA) is a measurement of the total surface area of the human body, expressed in square metres (m²). Unlike body weight, which reflects mass, BSA reflects the external size of a person and is a more reliable predictor of physiological processes such as cardiac output, basal metabolic rate, and drug distribution. In clinical medicine, BSA is used primarily for calculating chemotherapy doses, assessing the extent of burns, estimating renal glomerular filtration rate, and normalising cardiac measurements. Because BSA-based dosing accounts for differences in body size across patients, it helps clinicians prescribe drugs more precisely — reducing both the risk of toxic overdose in smaller patients and subtherapeutic underdose in larger ones. Multiple mathematical formulas have been developed over the past century to estimate BSA from height and weight, each with varying accuracy across different populations.
How to Use This Calculator
- 1. Choose your unit system — Metric (cm and kg) or Imperial (feet, inches, and pounds).
- 2. Enter your height and weight in the input fields provided.
- 3. Click Calculate BSA — the primary Mosteller result appears instantly alongside a comparison table of all 5 formulas.
BSA Formula Reference
Mosteller (1987)
BSA = √( H × W / 3600 )
Most widely used in clinical practice. Simple and easy to compute mentally.
DuBois & DuBois (1916)
BSA = 0.007184 × H⁰·⁷²⁵ × W⁰·⁴²⁵
Historically the first formula, derived from only 9 subjects. Still widely cited.
Haycock (1978)
BSA = 0.024265 × H⁰·³⁹⁶⁴ × W⁰·⁵³⁷⁸
Most accurate for both children and adults. Preferred in paediatric oncology.
Gehan & George (1970)
BSA = 0.0235 × H⁰·⁴²²⁴⁶ × W⁰·⁵¹⁴⁵⁶
Derived from a large dataset; commonly used in research contexts.
Boyd (1935)
BSA = 0.0003207 × H⁰·³ × W^(0.7285 − 0.0188 × log₁₀(W))
Developed for children; accounts for non-linear weight scaling via a logarithmic term.
H = height in cm, W = weight in kg for all formulas above.
Practical Example
For a person who is 175 cm tall and weighs 70 kg:
| Formula | BSA (m²) |
|---|---|
| Mosteller | 1.845 |
| DuBois & DuBois | 1.848 |
| Haycock | 1.868 |
| Gehan & George | 1.857 |
| Boyd | 1.862 |
Mosteller: √(175 × 70 / 3600) = √(3.4028) = 1.845 m². All five formulas produce very similar results for a person of average adult proportions.
Why BSA Matters in Medicine
-
•
Chemotherapy dosing: Most cytotoxic drugs are prescribed as mg/m². Multiplying this value by the patient's BSA gives the actual dose, helping to minimise toxicity in smaller patients and avoid underdosing larger ones.
-
•
Burn assessment: The Rule of Nines estimates the percentage of body surface area affected by burns, directly using BSA concepts to guide fluid resuscitation and transfusion decisions in burn units.
-
•
Renal clearance: Glomerular filtration rate (GFR) is normalised to a BSA of 1.73 m² (the average BSA used as a standardising reference) to allow comparison of kidney function across patients of different sizes.
-
•
Cardiac indices: Parameters like cardiac output and stroke volume are indexed to BSA to produce cardiac index and stroke volume index, allowing fair comparison between patients.
Comparison of BSA Formulas
| Formula | Year | Best For | Notes |
|---|---|---|---|
| Mosteller | 1987 | General clinical use | Simplest formula; most widely adopted worldwide |
| DuBois & DuBois | 1916 | Historical reference | First published formula; small original sample (n=9) |
| Haycock | 1978 | Children & adults | Most accurate across wide range; preferred in paediatrics |
| Gehan & George | 1970 | Research populations | Large dataset derivation; good general accuracy |
| Boyd | 1935 | Children | Logarithmic weight term handles low weight non-linearity well |
Frequently Asked Questions
What is a normal BSA?
The average BSA for an adult is approximately 1.7 m². Average adult males typically have a BSA of around 1.9 m², while average adult females are around 1.6 m². A healthy adult typically falls in the range of 1.5–2.2 m². BSA increases with height and weight, so taller or heavier individuals will have a larger BSA.
Which BSA formula is most accurate?
The Haycock formula is generally considered the most accurate across a wide range of patients, including children and adults. However, the Mosteller formula is the most commonly used in clinical settings due to its simplicity. For paediatric oncology, Haycock and Boyd are frequently preferred. In practice, the differences between formulas for typical adults are usually less than 2–3%.
Why is BSA used for chemotherapy dosing?
BSA is used because drug clearance and toxicity correlate better with body surface area than with weight alone. Chemotherapy agents are highly toxic and have narrow therapeutic windows. Dosing by BSA (in mg/m²) normalises the dose across patients of different sizes, helping reduce the risk of severe side effects in smaller patients while ensuring therapeutic efficacy in larger patients. Most oncology protocols therefore express doses per m² of BSA.
How is BSA different from BMI?
BMI (Body Mass Index) is calculated as weight (kg) divided by height² (m²) and is used to classify body weight relative to height (underweight, normal, overweight, obese). BSA measures the actual physical external surface area of the body in m² and is used for clinical dosing, burn assessment, and organ function normalisation. While BMI is a screening tool for weight-related health risk, BSA is primarily a pharmacological and physiological measurement tool.
Can I use this calculator for medication dosing?
This calculator provides BSA estimates for informational and educational purposes only. Actual medication dosing must always be determined by a qualified healthcare professional who will consider organ function, drug interactions, clinical condition, and other patient- specific factors. Never adjust or calculate your own drug doses based solely on this or any online tool.