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 = 1.810 m²
• Haycock: 0.024265 × 170^0.3964 × 70^0.5378 = 1.826 m²

For a prescribed dose of 500 mg/m², total dose using Mosteller = 909 mg. The same order under Haycock would be 913 mg, and under DuBois 905 mg: a spread of 8 mg on this patient, and under 1%. At average build the choice barely matters, which is exactly why people stop thinking about it. At the extremes it matters a great deal, and the calculator shows all three so the gap is visible before it is ignored.

Two different things both get called “capping”, and the calculator does both separately.

A hard BSA cap is the common one: many institutions cap BSA at 2.0 or 2.2 m² for certain agents, so a patient calculating at 2.4 m² is dosed as though they were 2.0. The cap only does anything if the patient is above it. Enter the ceiling in m², or leave it blank for none.

A flat percentage reduction is a different practice: the full calculated BSA is scaled down, often to 90% or 95%, usually as part of a protocol-specified dose reduction for toxicity or performance status. This applies to everyone regardless of size. Leave it at 100 for no reduction.

The two are not interchangeable, and the field on this page used to be labelled a cap while behaving as a percentage reduction. If both are set, the percentage is applied first and then the ceiling.

Other regimens sidestep the question by using ideal body weight or adjusted ideal body weight rather than actual weight to compute BSA in the first place. That is a protocol decision, not something to improvise.

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, so 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.