Body Surface Area (BSA) Calculator
Enter your height and weight to estimate your body surface area (BSA) using multiple validated formulas.
Reviewed by the ToolNestr Editorial Team — July 2026
Enter your height and weight to estimate BSA.
About body surface area
Body surface area is a critical metric in clinical medicine. Unlike weight alone, BSA accounts for both height and weight, making it a better indicator of metabolic mass. It is used to calculate chemotherapy dosages, glucocorticoid doses, cardiac output (as the cardiac index), glomerular filtration rate (kidney function), and burn surface area for fluid resuscitation. The Mosteller formula is the most widely used today because of its simplicity — it is simply the square root of height × weight divided by 3600 (or 3131 for imperial). This calculator provides three major formulas for comparison. For other body composition metrics, see the BMI Calculator and Lean Body Mass Calculator.
BSA estimates are for informational purposes. Medical decisions should be made by qualified healthcare professionals.
How it works
BSA formulas are all derived from height and weight using different mathematical relationships. The Mosteller formula uses a simple geometric mean (square root of height × weight divided by a constant). The Du Bois formula uses an exponential equation developed from direct measurements of nine subjects in 1916 — remarkably, it remained the standard for decades. The Haycock formula was developed in 1978 specifically to improve accuracy for children and infants. All three are shown for comparison; they typically agree within 5–10% for most adults.
The formulas explained
Mosteller (1987): BSA (m²) = √(height_cm × weight_kg / 3600)
Du Bois (1916): BSA = 0.007184 × weight^0.425 × height^0.725
Haycock (1978): BSA = 0.024265 × weight^0.5378 × height^0.3964
Worked example
A person measuring 175 cm tall and weighing 80 kg wants to know their BSA.
Oncology patient
Understand how BSA is used to calculate your chemotherapy dose. Knowing your BSA helps you have informed conversations with your oncologist.
Medical student
Compare the three major BSA formulas and understand why Mosteller is preferred in modern clinical practice for its simplicity.
Burn clinician
Use BSA to calculate the percentage of body surface area affected by burns — the basis for fluid resuscitation and transfer decisions.
Research scientist
Normalise physiological measurements (cardiac output, GFR) to BSA for accurate cross-subject comparisons in clinical research.
How to use this calculator
Enter your height
Measure your height accurately using a wall-mounted stadiometer if possible. Metric or imperial both work.
Enter your weight
Use your current body weight. For medical purposes, use a calibrated scale with minimal clothing.
Compare formulas
See your BSA from three major formulas. The Mosteller result is the highlighted one, as it is most commonly used in clinical practice today.
Tips for BSA interpretation
BSA changes slowly
Unlike weight, BSA changes slowly because height is fixed and weight changes must be significant to alter BSA substantially. A 5 kg weight change shifts BSA by only about 3–4%.
Formulas agree for most people
For adults of average height and weight, all three formulas give nearly identical results. Differences become more noticeable for very tall, short, heavy or very lean individuals.
BSA is not body fat
BSA does not measure body composition. Two people with the same height and weight have the same BSA regardless of their body fat percentage. Use the Body Fat Calculator for composition.
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Frequently asked questions
What is body surface area?
Body surface area (BSA) is the total external surface area of the human body, measured in square metres (m²). It is used in medicine for drug dosing, burn assessment and calculating cardiac output and renal function.
Which BSA formula is most accurate?
The Mosteller formula is the most widely used in clinical practice due to its simplicity and good accuracy for most adults. The Du Bois formula was the original standard. Haycock is preferred for children.
Why is BSA used for chemotherapy dosing?
Many chemotherapy drugs have a narrow therapeutic index — too little is ineffective, too much is toxic. BSA correlates better with metabolic processes than weight alone, making it a safer basis for dosing.
What is a normal BSA?
The average adult BSA is about 1.73 m² (range 1.5–2.0 m² for most adults). It varies with height, weight and body composition. Men typically have a higher BSA than women of the same height and weight.
Can I calculate BSA for children?
Yes — the Haycock formula is validated for children and infants. The Mosteller formula also works well for older children. For accurate paediatric dosing, always consult a healthcare provider.