Body Measurement Calculators

The body measurement calculator computes Body Surface Area (BSA) — the single derived measure that feeds many size-adjusted dosing and indexed hemodynamic calculations. BSA in m² is required for most chemotherapy regimens and for indexing cardiac output to cardiac index.

More body measurements will be added here over time (BMI, ideal body weight, lean body weight); the current page provides the BSA tool that the rest of the network's pediatric and oncology calculations depend on.

When to use these calculators

BSA appears in three common bedside contexts. First, dose-by-BSA for chemotherapeutic agents — most regimens prescribe in mg/m² rather than mg or mg/kg, so a patient's BSA is required before any dose is drawn. Second, pediatric dosing for medications that scale better by BSA than by body weight (some cardiac drugs, fluid maintenance estimates). Third, hemodynamic indexing — Cardiac Index (CI) is cardiac output divided by BSA, used to compare flow across patients of different body sizes. [REVIEW: confirm clinical use cases].

The calculator uses the Mosteller formula (BSA = √(Height × Weight ÷ 3600), height in cm, weight in kg), the most widely used clinical formula because it's simple and well-validated across adult and pediatric populations. Other formulas (Du Bois, Haycock, Boyd) typically agree within about 5%.

Frequently Asked Questions

Which BSA formula does this calculator use?

The Mosteller formula: BSA (m²) = √((Height in cm × Weight in kg) ÷ 3600). It's the most common formula in clinical practice because it's simple to compute, well-validated, and agrees with the older Du Bois and Boyd formulas to within about 5% across most patient sizes.

When does BSA differ enough between formulas to matter clinically?

For most adults of average size, Mosteller, Du Bois, Haycock, and Boyd all return BSAs within 0.05-0.10 m² of each other — clinically negligible. The formulas diverge more at extremes of body habitus (very small infants, obese patients), so verify against your institution's preferred formula when dosing high-risk medications in those populations. [REVIEW: confirm clinical thresholds].

Why is BSA used instead of body weight for chemo dosing?

Chemotherapeutic agents distribute more closely with BSA than with weight because tissue perfusion, drug clearance, and metabolic rate scale with surface area rather than mass. Dose-by-weight in oncology can produce significant under- or over-dosing relative to dose-by-BSA in patients of unusual body composition.

How does BSA relate to Cardiac Index?

Cardiac Index (CI) = Cardiac Output (CO) ÷ BSA. CI normalizes flow for body size, so a CO that looks normal for a small patient may be inadequate for a large patient, and vice versa. CI is the typical bedside hemodynamic target rather than CO alone.