Body Surface Area Calculators

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Body surface area (BSA) is a measure of the external surface of the human body, typically expressed in square meters (m²). Unlike body weight, BSA correlates more closely with metabolic rate, cardiac output, and drug distribution volume, making it a preferred basis for dosing chemotherapy agents and calculating cardiac indices. The average adult BSA is approximately 1.7–1.8 m². Several validated formulas — including Mosteller, DuBois, and Haycock — estimate BSA from height and weight and are used interchangeably in clinical practice.

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BSA Formulas

The most commonly used BSA formulas are:

  • Mosteller: BSA (m²) = √[(height cm × weight kg) / 3600] — simple and widely used in oncology
  • DuBois and DuBois: BSA = 0.007184 × height^0.725 × weight^0.425 — historical gold standard
  • Haycock: BSA = 0.024265 × height^0.3964 × weight^0.5378 — preferred in pediatrics
  • Boyd: BSA = 0.0003207 × height^0.3 × weight^(0.7285 − 0.0188 × log(weight)) — valid across wide weight range

BSA in Chemotherapy Dosing

Most cytotoxic chemotherapy drugs are dosed in mg/m². BSA-based dosing assumes that drug clearance scales with BSA, though this assumption is increasingly questioned. A 1.73 m² reference BSA is used for normalization in some contexts. Oncology guidelines differ on whether BSA should be capped at a maximum to avoid overdosing in obese patients.

BSA vs. Body Weight Dosing

Weight-based dosing (mg/kg) is simpler but correlates less well with pharmacokinetics for some agents. BSA-based dosing is preferred for drugs with narrow therapeutic windows where under- or overdosing has significant clinical consequences. For targeted therapies and immunotherapy agents, fixed dosing is increasingly common because therapeutic effect correlates better with receptor occupancy than with BSA.

Glossary

Body Surface Area (BSA)
The measured or calculated external surface of a human body in m²; used to normalize drug doses in oncology and physiological measurements like cardiac index.
Mosteller Formula
A widely used BSA formula: √[(height cm × weight kg) / 3600]; favored in oncology for simplicity and reasonable accuracy.
Cardiac Index
Cardiac output normalized to BSA (L/min/m²); used to compare heart function between patients of different body sizes.

Frequently Asked Questions

The Mosteller formula is: BSA (m²) = √[(height in cm × weight in kg) / 3600]. It is the most widely used formula in oncology for its simplicity and acceptable accuracy. For a patient who is 170 cm tall and weighs 70 kg: BSA = √[(170 × 70) / 3600] = √(3.306) ≈ 1.82 m².

BSA correlates with several physiological parameters — including renal glomerular filtration rate, cardiac output, and liver blood flow — that determine drug distribution and clearance. Dosing in mg/m² aims to achieve consistent drug exposure across patients of different sizes, reducing variability in both toxicity and therapeutic effect. However, recent evidence suggests other pharmacokinetic approaches may be more accurate for some agents.

The average BSA is approximately 1.7–1.8 m² for adult women and 1.9 m² for adult men, with 1.73 m² often used as the standard reference for normalizing physiological measurements. Actual values vary substantially based on height and weight. Pediatric BSA is significantly smaller — a newborn is approximately 0.25 m² and a 10-year-old approximately 1.1 m².

The Haycock formula is considered the most accurate BSA estimate across a wide pediatric age range, from premature neonates to adolescents. The Gehan-George formula is also validated for pediatric use. The DuBois formula, designed for adults, can overestimate BSA in small children. Accurate BSA is especially important in pediatric oncology, where dosing errors carry significant risk.