Body Surface Area Calculator

About the Body Surface Area Calculator

A body surface area (BSA) calculator estimates the total skin surface area of a human body in square metres using height and weight, applying the Mosteller and DuBois formulas — the two most widely used clinical standards. BSA is a critical parameter in medicine because it correlates better than body weight with metabolic rate, cardiac output, and drug distribution volume for many medications. Chemotherapy drug doses are routinely calculated in mg/m² of BSA rather than mg/kg of body weight, because this reduces inter-patient variability in drug exposure. The Mosteller formula (BSA = √(H_cm × W_kg / 3600)) is used in most modern clinical practice due to its simplicity; the DuBois formula (0.007184 × H_cm^0.725 × W_kg^0.425), published in 1916, was historically standard and remains in use for comparison. Average BSA values: adult male ~1.9 m², adult female ~1.6 m², reference value used in many drug calculations = 1.73 m². This calculator is essential for oncologists, clinical pharmacists, burn specialists, intensivists, and medical students. In health, fitness, and nutritional planning, tracking personal metrics provides a scientific, data-driven baseline for setting realistic wellness goals. Human metabolism and body composition are highly individual, influenced by factors such as age, biological sex, height, activity level, and underlying genetics. While standard equations (such as the Mifflin-St Jeor or Navy Body Fat equations) offer valuable population-level screening guidelines, they should be interpreted alongside other markers of health under the guidance of qualified professionals. Using this calculator allows you to monitor changes over time, helping you calibrate your daily caloric intake, macronutrient balance, or hydration schedule to support sustainable lifestyle improvements and long-term vitality. Furthermore, individual circumstances and local regulations can significantly impact the practical application of these figures. Users in the USA, Canada, the United Kingdom, Australia, and New Zealand often face different regional guidelines, tax brackets, or baseline measurements (such as USDA zones, CRA guidelines, HMRC allowances, or ATO schedules) that should be factored into any serious planning. By entering your specific parameters into this calculator, you can model multiple scenarios side by side to see how minor changes in inputs affect the overall outcome. This makes the tool an indispensable asset for regular monitoring and long-term goal setting, helping you adjust your strategies as your needs evolve over time.

How It Works

Mosteller: BSA (m²) = √(H_cm × W_kg / 3600). Equivalent: √((H_in × W_lb) / 3131). DuBois: BSA (m²) = 0.007184 × H_cm^0.725 × W_kg^0.425. Haycock (often used in paediatrics): 0.024265 × H_cm^0.3964 × W_kg^0.5378. Example — 175 cm, 70 kg male. Mosteller: √(175 × 70 / 3600) = √(12250/3600) = √3.403 = 1.844 m². DuBois: 0.007184 × 175^0.725 × 70^0.425 = 0.007184 × 54.89 × 7.267 = 1.868 m². The two formulas agree within 1.3% for this typical adult. Chemotherapy dosing example: drug dosed at 50 mg/m². For 1.85 m² BSA: dose = 50 × 1.85 = 92.5 mg (rounded to nearest 10 mg or 5 mg per protocol). Burn rule of nines: head = 9%, each arm = 9%, chest = 18%, abdomen = 18%, each leg = 18%, perineum = 1% = total 100% BSA. To compute this value manually, follow these standard steps: 1. Identify all the required input variables (such as base values, rates, dimensions, or constants) and convert them to matching units. 2. Apply the primary mathematical formula or conversion factor designated for this specific calculation. 3. Perform the arithmetic operations step by step, ensuring you strictly follow the standard order of operations (PEMDAS/BODMAS). 4. Verify the result by running the calculation in reverse or checking against known reference tables. By following this structured methodology, you can verify your results and gain a deeper understanding of the relationships between the different variables involved in the calculation.

Tips & Best Practices

• ✓For chemotherapy dosing, most centres cap BSA at 2.0-2.2 m² for obese patients, using actual body weight for some agents and adjusted or ideal weight for others. Always follow the specific protocol or institutional guidelines rather than applying BSA mechanically — some drugs use flat dosing, weight-based dosing, or capped BSA.
• ✓The "reference man" BSA of 1.73 m² (170 cm, 70 kg) is used as a normalisation factor in cardiac physiology. Cardiac index = Cardiac output (L/min) / BSA (m²). Normal cardiac index is 2.5-4.0 L/min/m². Reporting cardiac output per BSA removes the effect of body size on the measurement.
• ✓Paediatric dosing: the Haycock formula (published 1978) is recommended for children because it was developed from measurements of subjects across a wider age and size range. Paediatric drug doses are often expressed per m² for chemotherapy and per kg for other medications — check which metric the prescribing reference uses.

Who Uses This Calculator

Oncologists and clinical pharmacists calculating chemotherapy drug doses from patient height and weight. Burn unit clinicians estimating percent body surface area burned for fluid resuscitation calculations (Parkland formula). Medical students and nursing students learning BSA-based dosing principles and practising clinical calculations. Intensivists calculating cardiac index from measured cardiac output and patient BSA. Common practical scenarios for this tool include: - Professional scenarios: Engineers, financial analysts, accountants, health practitioners, and educators use this calculation to verify data, draft official reports, and double-check manual calculations quickly. - Consumer and everyday scenarios: Homeowners, students, fitness enthusiasts, and travelers use the tool to make quick estimates on the go, budget for upcoming projects, and track personal goals. - Educational learning: Students and teachers use this tool as a step-by-step visual aid to understand mathematical formulas and verify homework answers.