Chemotherapy BSA Dose Calculator

Many chemotherapy drugs are dosed by body surface area rather than weight, because BSA correlates better with cardiac output, blood volume, and renal clearance — the variables that drive drug pharmacokinetics. The dose is prescribed as milligrams per square meter (mg/m²), and the calculator converts this into a concrete total milligram dose for a specific patient.

Three BSA formulas are widely used. They give similar results for adults of average build, but diverge slightly at extremes of weight and height:

Mosteller (1987): BSA = sqrt(height_cm × weight_kg / 3600) The simplest formula and the most commonly used in oncology clinics today. Trivial to compute mentally if you know square roots.

DuBois & DuBois (1916): BSA = 0.007184 × height^0.725 × weight^0.425 The original formula, derived from cadaver measurements of nine subjects. Still cited in most pharmacology references. Tends to slightly underestimate BSA in obese patients.

Haycock et al. (1978): BSA = 0.024265 × height^0.3964 × weight^0.5378 Developed specifically for pediatric patients across a wide age range. Often preferred in pediatric oncology and nephrology.

Once BSA is known, total dose = dose per m² × BSA.

Example: a patient measuring 170 cm, 70 kg.

• Mosteller: sqrt(170 × 70 / 3600) = sqrt(3.306) = 1.818 m²
• DuBois: 0.007184 × 170^0.725 × 70^0.425 = 1.811 m²
• Haycock: 0.024265 × 170^0.3964 × 70^0.5378 = 1.815 m²

For a prescribed dose of 500 mg/m², total dose using Mosteller = 909 mg.

Dose capping: many institutions cap BSA at 2.0 or 2.2 m² for some agents to limit toxicity in obese patients. Other regimens use ideal body weight or adjusted ideal body weight rather than actual weight to compute BSA. The calculator’s optional cap percentage applies a flat reduction to the calculated BSA before computing the dose. Set to 100 for no cap.

Why these distinctions matter: the wrong BSA formula or an uncapped dose in a very obese patient can cause significant overdosing of agents with narrow therapeutic indices. The wrong formula in a very thin or pediatric patient can underdose. Most modern protocols specify which formula to use; if unclear, Mosteller is the default standard.

Limitations and cautions:

• This calculator is a math helper, not a prescribing tool. Specific protocols, dose modifications for organ function (renal/hepatic), age-related adjustments, and cycle timing are determined by the prescribing oncologist.
• Carboplatin uses the Calvert equation (target AUC × (GFR + 25)) instead of mg/m² dosing — use a dedicated Calvert calculator for carboplatin.
• Dose rounding to the nearest convenient vial size is a separate clinical step that varies by drug and institution.
• The patient’s height, weight, and any recent significant weight changes should be verified before each cycle, not just at treatment start.