Clinical & Medical

Body Surface
Area Calculator

Calculate BSA using 5 validated formulas — DuBois, Mosteller, Haycock, Boyd, and Gehan-George. Includes drug dosing reference, cardiac index, and clinical uses guide.

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BSA (m²)

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Formula

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What Is Body Surface Area (BSA)?

Body Surface Area (BSA) is the total surface area of the human body, expressed in square meters (m²). It is used clinically to normalize drug doses, cardiac output measurements, and metabolic parameters — particularly important when body size varies significantly between patients, such as in pediatrics and oncology.

The 5 BSA Formulas

DuBois & DuBois (1916): BSA = 0.007184 × W^0.425 × H^0.725 Mosteller (1987) — Most widely used: BSA = √(H × W / 3600) Haycock (1978) — Best for children: BSA = 0.024265 × W^0.5378 × H^0.3964 Boyd (1935) — Best for neonates: BSA = 0.0003207 × W^(0.7285 − 0.0188×log(W)) × H^0.3 Gehan & George (1970): BSA = 0.0235 × W^0.51456 × H^0.42246 W = Weight in kg, H = Height in cm Average adult BSA: ~1.73 m² (range: 1.5–2.2 m²)

⚠️ Medical Disclaimer: This calculator is provided for educational purposes only. Drug dosing calculations based on BSA must be verified and prescribed by a qualified healthcare professional. Never adjust medication based solely on calculator outputs.

Frequently Asked Questions

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

Body surface area correlates better with many physiological parameters — cardiac output, renal function, and metabolic rate — than body weight alone. For chemotherapy agents with narrow therapeutic windows, BSA-based dosing reduces both under-dosing (ineffective treatment) and over-dosing (toxicity) compared to weight-based dosing. However, BSA-based dosing has limitations: it doesn't account for organ function, age-related pharmacokinetic changes, or obesity in some patients.

What is a normal BSA for adults?

The average BSA used as a reference standard in clinical medicine is 1.73 m² (based on a reference adult of ~70 kg and ~170 cm). In practice, BSA ranges from about 1.5 m² for small adults to 2.2+ m² for large adults. Many clinical calculations and lab reference ranges are normalized to 1.73 m² — for example, GFR is reported per 1.73 m² of BSA.

How does BSA relate to cardiac index?

Cardiac Index (CI) = Cardiac Output (CO) ÷ BSA. Normal CI is 2.5–4.0 L/min/m². Dividing by BSA normalizes for body size, making cardiac function comparable across patients. A cardiac output of 4.0 L/min in a 1.5 m² patient would give CI = 2.67 (normal), while the same CO in a 2.2 m² patient gives CI = 1.82 (low). This is why CI is clinically more useful than raw cardiac output.

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