Body Surface Area (BSA) Calculator – Du Bois, Mosteller & Haycock 🌎

How to calculate body surface area

The quickest way is the Mosteller formula — just a square root:

BSA (m²) = √(weight(kg) × height(cm) / 3600)

Step-by-step example: 70 kg, 170 cm → √(70 × 170 / 3600) = √(11900 / 3600) = √3.306 = 1.82 m²

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The 3 formulas

Mosteller (1987) — most widely used today

BSA = √(weight(kg) × height(cm) / 3600)

Published in the New England Journal of Medicine. Favored in oncology and clinical pharmacology for its simplicity and accuracy — you can calculate it on a basic calculator. Differences vs. Du Bois are typically <2% in adults within normal weight ranges.

Du Bois & Du Bois (1916) — the original

BSA = 0.007184 × weight(kg)^0.425 × height(cm)^0.725

Derived from only 9 subjects, yet became the reference for over 70 years. Most GFR normalization tables and cardiac output norms were built using this formula — which matters when you're interpreting older lab reports.

Haycock (1978) — preferred in pediatrics

BSA = 0.024265 × weight(kg)^0.5378 × height(cm)^0.3964

Validated on 81 subjects including infants and children. It outperforms Du Bois in extreme body sizes because it was calibrated on a broader weight/height range. Most pediatric drug dosing protocols specify this formula explicitly.

> Which formula should you use? Follow whatever is specified in the clinical protocol. Never switch formulas mid-treatment — a 3–5% difference between formulas can translate to a meaningful dose change in chemotherapy.

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BSA reference table (Mosteller)

Weight	Height	BSA (m²)
3 kg	50 cm	0.20
15 kg	95 cm	0.63
40 kg	150 cm	1.29
60 kg	165 cm	1.66
70 kg	170 cm	1.82
75 kg	175 cm	1.91
80 kg	180 cm	2.00
100 kg	185 cm	2.27

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Average BSA by group

Group	Average BSA (m²)
Newborn	0.25
2-year-old child	0.50
10-year-old child	1.14
Adult female	1.60–1.80
Adult male	1.80–2.00
Reference adult (GFR)	1.73

The 1.73 m² reference is the population average BSA established from early 20th-century studies. It remains the international standard for normalizing GFR regardless of which BSA formula you actually used to calculate it.

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Medical applications

Chemotherapy: doses are written in mg/m². Example: docetaxel 75 mg/m². If your BSA is 1.9 m², the prescribed dose is 75 × 1.9 = 142.5 mg. This matters because under-dosing reduces efficacy and over-dosing increases toxicity — the therapeutic window for many cytotoxics is narrow.

Cardiac index: cardiac output (L/min) ÷ BSA. Normal range: 2.5–4.0 L/min/m². A cardiac output of 5 L/min is normal in a 1.73 m² person but indicates hyperdynamic circulation in someone with 1.3 m².

Glomerular filtration rate (GFR): reported per 1.73 m² of body surface area. This normalization allows comparison across patients of different sizes — a GFR of 90 mL/min means something different in a 50 kg woman vs. a 100 kg man.

Burn surface area: clinical burn management uses the Rule of Nines (not BSA formulas) to estimate the percentage of skin affected — a different concept entirely.

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What BSA does NOT measure

Body fat percentage — a 90 kg athlete and a 90 kg sedentary person with the same height have identical BSA but very different pharmacokinetics for lipophilic drugs.

Metabolic rate — BSA correlates with basal metabolic rate (Rubner's surface law), but BMI or direct calorimetry are used clinically for that purpose.

Renal function — BSA normalizes GFR; it doesn't measure kidney function itself.

Obesity adjustment — most BSA formulas were validated on populations with normal BMI. In morbidly obese patients, some oncology protocols cap BSA at 2.0 m² or use adjusted/ideal body weight, precisely because the formulas weren't validated at the extremes.

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Common errors

Using height in meters instead of centimeters in the Mosteller formula — the result will be completely wrong.

Mixing formulas between dose calculation and protocol specification.

Using BSA for pediatric anesthesia drug dosing when weight-based (mg/kg) dosing is actually indicated — not all pediatric drugs are BSA-dosed.

Assuming BSA = body weight normalization — two patients with the same BSA can have very different weights if one is short and stocky vs. tall and lean.

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> ⚠️ This calculator is for informational purposes only. Drug doses, GFR interpretation, and clinical decisions must always be confirmed by a licensed healthcare professional using validated clinical protocols.