BSA in clinical practice: when weight isn't enough
Body weight scales drug dosing reasonably well for most medications. But for chemotherapy agents, the relationship between body weight and drug distribution is complex enough that body surface area became the standard dosing metric in oncology. The logic: BSA correlates with cardiac output, glomerular filtration rate and hepatic blood flow, all of which affect drug clearance.
Which formula to use
Mosteller (1987) is the most used in modern clinical practice: BSA (m²) = √(height cm × weight kg / 3600). Simple, accurate and widely validated. Use this unless your institution or protocol specifies otherwise. DuBois (1916) is the original formula and remains common in renal dosing references: BSA = 0.007184 × height cm^0.725 × weight kg^0.425. Haycock (1978) is preferred for paediatrics and neonates because it was validated specifically in children. Gehan-George (1970) and Boyd are alternatives used in specific contexts. A multicentre UK study of over 3,600 adult cancer patients found average measured BSA running higher than the historical 1.73 m² reference figure, a reminder that population-derived constants drift over time.
The differences between formulas are usually less than 5%, which translates to minor dose differences in practice. What matters most is consistency: use the same formula as the protocol you're following.
Dose capping in chemotherapy
Most intravenous chemotherapy drugs are dosed in mg/m². A patient with a BSA of 1.8 m² prescribed carboplatin at 200 mg/m² receives 360 mg. Dose capping is common: many protocols cap the dose at a BSA of 2.0 m² regardless of actual BSA, to avoid excessive toxicity in large patients. Always check the specific protocol for capping rules. Pair this with our Max Daily Dose Checker and Creatinine Clearance Calculator (used in Calvert formula for carboplatin dosing).
Chemotherapy during pregnancy
Chemotherapy during pregnancy is a rare but real clinical scenario, most often when cancer is diagnosed after conception. BSA-based dosing calculations don't change, but drug selection is severely restricted to agents with an established pregnancy safety profile. Use our Pregnancy Drug Safety Checker alongside this calculator when BSA dosing is required in a pregnant patient.
BSA in paediatric dosing
BSA-based dosing is sometimes used for paediatric medications when mg/kg dosing would result in adult doses being exceeded. In oncology, paediatric chemotherapy protocols almost universally use BSA for dosing. Some paediatric formulations are now supplied as ready-to-use, fixed-strength containers rather than individually compounded doses, a practice the FDA's guidance on labelling weight- and BSA-based dosing calls dose banding, which trades a small deviation from the exact calculated dose for simpler, lower-error administration.