Body Surface Area (BSA) Calculator
Body Surface Area (BSA) Calculator
Calculate BSA by the Mosteller or Du Bois formula, the basis of most chemotherapy dosing and of eGFR indexing.
Body Surface Area (BSA)
Height & weightHeight 172 cm, weight 78 kg, Mosteller formula
Formula
Du Bois: BSA = 0.007184 × height (cm)^0.725 × weight (kg)^0.425
- Mosteller
- the default here — arithmetically simple and now the most widely used formula in practice
- Du Bois
- published in 1916, derived from direct surface measurement in nine subjects, one of them a child
Worked example
Height 172 cm, weight 78 kg, Mosteller formula
172 × 78 = 13,416
13,416 ÷ 3600 = 3.7267
√3.7267 = 1.93 m²
The Du Bois formula gives 1.91 m² for the same patient — the two formulae typically agree within about 1–2%
Mosteller vs Du Bois for this patient
| Formula | BSA |
|---|---|
| Mosteller | 1.93 m² |
| Du Bois | 1.91 m² |
What BSA is used for, and where it falls short
BSA is the basis of most cytotoxic chemotherapy dosing and of the Calvert formula used to dose carboplatin from target AUC and GFR, and it is also what indexes eGFR to a standard 1.73 m² so that patients of different sizes can be compared on the same scale. Almost every intravenous chemotherapy regimen still prescribes a dose in mg per m² rather than a flat dose or a per-kilogram dose.
Mosteller’s formula is the square root of height in cm times weight in kg, divided by 3600 — simple enough to calculate mentally at the bedside, and it is now the most widely used version in clinical practice. Du Bois dates from 1916 and was derived by direct surface measurement in nine subjects, one of them a child, using a method that would not meet modern standards, though it remains in use and produces results within a percent or two of Mosteller’s for most adults.
BE CANDID about the underlying weakness: BSA correlates poorly with actual drug clearance for most chemotherapy agents, and the practice of dosing by BSA persists largely by historical convention rather than strong pharmacokinetic evidence — clearance depends on renal and hepatic function, body composition and drug-specific factors that BSA only crudely approximates.
One practical point matters directly for safety: ASCO guidance recommends using actual body weight rather than capping BSA at 2.0 m² in obese patients, because capping systematically underdoses this group and has been associated with worse outcomes. Older practices of capping at 2.0 m² should not be applied by default.
Frequently asked questions
Which BSA formula should I use — Mosteller or Du Bois?
Mosteller is the default in most modern practice: it is simpler and gives results very close to Du Bois for typical adults. Some institutions specify Du Bois by protocol, so check local convention for chemotherapy dosing.
Why is chemotherapy dosed by body surface area?
It is a long-standing convention intended to normalise dosing across patients of different sizes, and it remains the basis of most cytotoxic regimens and of the Calvert formula for carboplatin, though it correlates only weakly with actual drug clearance.
Should BSA be capped at 2.0 m² for obese patients?
No. ASCO guidance recommends dosing on actual body weight rather than capping BSA at 2.0 m², because capping systematically underdoses larger patients and worsens outcomes.
What else is BSA used for besides chemotherapy?
It is also used to index eGFR to a standard 1.73 m², allowing kidney function to be compared across patients of different sizes, and appears in various cardiac and burns calculations.
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References
- Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098.
- Griggs JJ et al. Appropriate systemic therapy dosing for obese adult patients with cancer: ASCO guideline update. J Clin Oncol. 2021;39(18):2037–48.