Body Surface Area Calculator

Body Surface Area Calculator

Body Surface Area Calculator

Body Surface Area (BSA) Calculator

The calculator below estimates the body surface area (BSA), which is the total external surface of the human body. Since direct measurement is complex, researchers have developed various mathematical formulas to approximate BSA. This tool applies several of the most widely used equations.

Average Body Surface Area Values

Group ft² m²
Newborn 2.69 0.25
2-year-old child 5.38 0.50
10-year-old child 12.27 1.14
Adult woman 17.22 1.60
Adult man 20.45 1.90

Why BSA Matters

In medicine, BSA is often preferred over weight alone because it gives a better reflection of metabolic mass—the body’s active tissue that requires energy. Metabolic mass excludes fat, since fat tissue is not metabolically active, and instead includes lean tissues like muscles, bones, blood, organs, and nerves.

Clinical Applications of BSA
  • Chemotherapy dosing: BSA is commonly used to determine drug dosages in cancer treatments.
  • Cardiology: Helps calculate cardiac index, which adjusts heart performance for body size.
  • Metabolic estimates: Provides a closer approximation of the body’s energy needs than body weight.

While BSA is useful, it isn’t perfect. For medications with a narrow therapeutic index (where the safe and toxic doses are close), BSA-based dosing can sometimes be inaccurate. It may also be less reliable in very short, tall, underweight, or obese patients, where BMI or other measures may be more suitable. Still, BSA remains more consistent than body weight for many drug calculations.

Common BSA Formulas

Each formula uses weight (W in kg) and height (H in cm) to estimate BSA in square meters (m²).

  • Du Bois Formula (1916) BSA = 0.007184 × W0.425 × H0.725 One of the earliest and most commonly used formulas, effective for both lean and obese patients.
  • Mosteller Formula (1987) BSA = 0.016667 × W0.5 × H0.5 Simple and widely used due to ease of calculation.
  • Haycock Formula (1978) BSA = 0.024265 × W0.5378 × H0.3964 Validated across infants, children, and adults.
  • Gehan & George Formula (1970) BSA = 0.0235 × W0.51456 × H0.42246 Originally developed for chemotherapy dosing.
  • Boyd Formula (1935) BSA = 0.03330 × W(0.6157 − 0.0188 × log10W) × H0.3 Accounts for body composition by including a weight-adjusted factor.
  • Fujimoto Formula (1968) BSA = 0.008883 × W0.444 × H0.663 Derived from studies of Japanese populations.
  • Takahira Formula (1968) BSA = 0.007241 × W0.425 × H0.725 Another formula from Japanese research, similar in structure to Du Bois.
  • Fujimoto Formula (1968) BSA = 0.008883 × W0.444 × H0.663 Derived from studies of Japanese populations.
  • Schlich Formula
    • Women: BSA = 0.000975482 × W0.46 × H1.0 Adjusts for sex-specific differences in body composition.