BSA Calculator

⚕️ Not medical advice. This is general information for healthy adults and does not replace a doctor, dietitian or other health professional. Speak to one before acting on a result, especially if you are pregnant, have a medical condition or are worried about a symptom.

BSA formulas compared

This calculator provides results from all four major BSA formulas so you can compare them and choose the most appropriate one for your clinical context:

Mosteller (1987): BSA = √(H × W / 3600) — simple, accurate, most widely used in oncology
Du Bois & Du Bois (1916): BSA = 0.007184 × H^0.725 × W^0.425 — oldest formula, based on 9 subjects; still widely cited
Haycock (1978): BSA = 0.024265 × H^0.3964 × W^0.5378 — validated for paediatric populations
Boyd (1935): BSA = 0.0003207 × H^0.3 × (W×1000)^(0.7285 − 0.0188 log(W×1000)) — some references prefer it (or Haycock) for infants and neonates

Clinical applications of BSA

Chemotherapy dosing: Many cancer drugs are dosed in mg/m² of BSA, although some, such as carboplatin, are usually dosed by a target AUC (Calvert formula) rather than by BSA. Dosing is decided by the treating oncology team.
Cardiac index: CI = Cardiac Output (L/min) ÷ BSA (m²). Normal range: 2.5–4.0 L/min/m².
Burns assessment: The Rule of Nines estimates the percentage of BSA affected by burns to guide fluid resuscitation.

⚠️ This calculator is for informational purposes only. All medical dosing decisions must be made by qualified healthcare professionals.

Interpreting your BSA result

For an average adult, a BSA between 1.6 m² and 2.0 m² is considered normal. A 170 cm, 70 kg adult has a BSA of approximately 1.82 m² using the Mosteller formula, originally published in the New England Journal of Medicine (1987). Paediatric BSA values range from about 0.25 m² at birth to 1.14 m² at age 10 and 1.60 m² by adolescence.

In oncology, many chemotherapy doses are calculated as mg/m² of BSA. As a purely illustrative example, a dose of 60 mg/m² for a patient with a BSA of 1.8 m² works out to 108 mg in total; actual doses depend on the drug, regimen and patient, and are decided by the treating oncology team. BSA-based dosing is intended to reduce variability between patients of different sizes.

When body weight is preferred over BSA

While BSA is standard for many chemotherapy agents, some drugs are dosed by actual body weight (mg/kg) or ideal body weight — particularly antibiotics, anticoagulants like heparin, and renally-cleared drugs where GFR matters more than surface area. Always refer to current pharmacology guidelines and consult a clinical pharmacist when calculating doses for obese patients, where actual BSA can significantly overestimate appropriate dosing.

Frequently asked questions

What is Body Surface Area (BSA)?

Body Surface Area (BSA) is a measurement of the total surface area of the human body, expressed in square metres (m²). It is often preferred over body weight for some clinical calculations because it is thought to track metabolic mass more closely, although it does not measure body composition directly.

Why is BSA used in medicine?

BSA is widely used for calculating chemotherapy drug doses, where dosing errors can be life-threatening. It is also used for calculating cardiac index (cardiac output normalised to BSA), glomerular filtration rate in paediatrics, caloric requirements, and burn area assessments.

Which BSA formula is most accurate?

The Mosteller formula (1987) is the most commonly used in modern clinical practice due to its simplicity and good accuracy: BSA = √(height × weight / 3600). The Du Bois formula (1916) is older but still widely cited in literature. Some references prefer the Haycock formula for paediatric patients, and some prefer Boyd or Haycock for infants and neonates.

What is the average BSA for an adult?

The average BSA for a healthy adult male is approximately 1.9 m² and for an adult female approximately 1.6 m². Paediatric values range from 0.25 m² for neonates to 1.14 m² for 10-year-olds. These values are used as standards in drug dosing guidelines.

What is the Mosteller formula?

The Mosteller formula is: BSA (m²) = √(Height (cm) × Weight (kg) / 3600). It is simple, accurate, and widely adopted in oncology protocols. For a person 170 cm tall weighing 70 kg: BSA = √(170 × 70 / 3600) = √3.306 ≈ 1.818 m².