BSA — Mosteller vs DuBois vs Haycock vs Boyd, and Which to Use When
Body surface area (BSA) shows up in three places in clinical practice:
- Chemotherapy dosing — almost everything in oncology is mg/m²
- Cardiac index — cardiac output normalised to body size
- Pediatric drug dosing — for some agents where weight-based dosing isn't enough
There are at least eight published formulas for estimating BSA from height + weight. The four you'll see most often are Mosteller, DuBois, Haycock, and Boyd. They all give slightly different answers — typically within 5% of each other for adults — but the choice of formula is institutional, and using the wrong one can technically be a med error if the order specifies one.
The four formulas
Mosteller (1987)
BSA (m²) = √((height_cm × weight_kg) / 3600)
The modern default. Fast, simple, mental-math friendly. Validated in adults and most pediatric ages. Most clinical institutions use Mosteller for chemo unless protocol specifies otherwise.
DuBois & DuBois (1916)
BSA (m²) = 0.007184 × W_kg^0.425 × H_cm^0.725
The original. Still cited in pharmacology references and some clinical guidelines by tradition. Tends to slightly underestimate BSA in obese patients compared to Mosteller.
Haycock (1978)
BSA (m²) = 0.024265 × W_kg^0.5378 × H_cm^0.3964
Specifically validated in children and infants. Pediatric units often use Haycock. The coefficients give it slightly different scaling at the low end of weight.
Boyd (1935)
BSA (m²) = 0.0003207 × H_cm^0.3 × (W_g)^(0.7285 - 0.0188 × log10(W_g))
The most complex. Mostly used in older texts and certain research contexts.
A worked example
70 kg, 170 cm adult: - Mosteller: √((170 × 70) / 3600) = √3.306 = 1.819 m² - DuBois: 0.007184 × 70^0.425 × 170^0.725 = 1.812 m² - Haycock: 0.024265 × 70^0.5378 × 170^0.3964 = 1.819 m² - Boyd: ~1.838 m²
Three formulas agree to within a tenth of a percent; Boyd is about 1% higher. For a 100 mg/m² chemo dose, that's 182 mg vs 184 mg — clinically not a difference, but worth picking the right formula and being consistent.
When the formulas disagree more
The four formulas diverge most at the extremes:
- Very small infants — Haycock was designed for this range and tends to give the most accurate values.
- Very obese patients — DuBois and Boyd tend to overestimate; Mosteller is the most defensible. Some institutions cap BSA at 2.0 m² or 2.2 m² for chemo dosing in severe obesity, or use ideal vs actual body weight depending on the agent.
- Pediatric oncology — the choice between Mosteller and Haycock can shift a dose by a few percent. Institutional protocol decides.
The "which one does my hospital use" question
When in doubt: ask your pharmacist. Chemo BSA in particular is something pharmacy will have a defined SOP for, and they'll know exactly which formula is in the order set. The wrong formula in a chemo dose calculation is the kind of thing the second pharmacist's check catches — but easier to get right the first time.
For non-chemo uses (cardiac index, occasional pediatric dosing), Mosteller is almost always fine.
The mg/m² rationale
Why dose by surface area at all? The argument, dating back to early oncology, is that drug clearance correlates better with surface area than with weight alone — surface area approximates lean body mass + organ size more closely than weight does. The evidence has been challenged for many specific agents (some chemo agents arguably should be weight-dosed or AUC-dosed), but mg/m² remains the dominant convention because changing institutional practice is hard and most regimens have decades of dose-finding data tied to it.
Skip the calculator
The BSA Calculator computes all four formulas at once, with imperial OR metric input, so you can compare at a glance and pick what your institution uses. Inline guidance on which fits when. Same on-device privacy as the rest of the /health suite.
The short version
Mosteller is the modern default and what you should reach for unless a protocol says otherwise. Haycock for pediatrics. DuBois and Boyd for historical reference and the rare order that specifies them. The four agree to within ~5% in normal-range adults; the choice matters most at the extremes (very small, very large) and most clinically when the dose is sharp (chemo).