Body Surface Area Calculator
Calculate your body surface area (BSA) using five validated medical formulas (Mosteller, Du Bois, Haycock, Boyd, and Gehan & George). Get an averaged BSA, a chart comparison, and BMI reference — all for free.
What Is Body Surface Area (BSA)?
Body surface area (BSA) is the total surface area of the human body, usually expressed in square meters (m²). In medicine, BSA is a more reliable index of metabolic mass than body weight alone — which is why it's used to calculate doses for chemotherapy, determine cardiac index, assess burn injuries, and dose certain medications (e.g., corticosteroids and biologics).
For the average adult, BSA is roughly 1.6 – 2.0 m². This calculator computes BSA using five validated formulas and shows both each individual result and their average.
The Five BSA Formulas Used
Mosteller (1987) — most widely used:
BSA (m²) = √( height(cm) × weight(kg) ÷ 3600 )
Du Bois (1916) — the classic reference:
BSA (m²) = 0.007184 × height(cm)0.725 × weight(kg)0.425
Haycock (1978) — well-validated in children:
BSA (m²) = 0.024265 × height(cm)0.3964 × weight(kg)0.5378
Boyd (1935) — weight-logarithmic:
BSA (m²) = 0.0003207 × height(cm)0.3 × weight(g)(0.7285 − 0.0188 × log₁₀ weight(g))
Gehan & George (1970) — modern regression:
BSA (m²) = 0.0235 × height(cm)0.42246 × weight(kg)0.51456
All five formulas take only height and weight as inputs — BSA is therefore gender-neutral. The calculator uses your selected unit system and automatically converts to metric before applying the formulas.
Why Use This BSA Calculator?
- Five formulas at once: Compare results and see how much they agree.
- Average BSA: A robust value that smooths formula-specific quirks.
- Chart comparison: A bar chart shows how each formula's estimate differs.
- BMI reference: See your BMI alongside your BSA to interpret results in context.
- Clinical-grade precision: Up to 4 decimal places for research or dosing purposes.
- Free & Private: No registration, no data storage.
Understanding Your BSA Results
- Typical adult range: 1.6 – 2.0 m². Values outside this range may indicate high or low body mass for height.
- Children and adolescents: BSA is smaller — around 0.5 m² at age 1, 1.0 m² at age 7, and 1.7 m² by age 15. Haycock's formula is particularly well-validated in children.
- Very tall or very heavy adults: BSA may exceed 2.2 m².
- Very small adults: BSA may fall below 1.4 m².
BMI is shown as a secondary reference because BSA does not have universal "healthy" thresholds — but BMI-based categories help you interpret whether your BSA is being driven by healthy or excessive mass.
Where BSA Is Used in Medicine
- Chemotherapy dosing: Most cytotoxic drugs are dosed in mg/m² of BSA.
- Cardiac index: Cardiac output is indexed to BSA (L/min/m²) to compare patients of different sizes.
- Burn assessment: The "Rule of Nines" and Lund-Browder charts estimate burn area as a percentage of BSA.
- Glomerular filtration rate (GFR): Often normalized to 1.73 m² of BSA.
- Drug dosing: Certain biologics, corticosteroids, and pediatric medications are dosed by BSA.
Note: BSA formulas are population averages. For clinical decisions — especially chemotherapy dosing — always use the formula specified by your institution's protocol. This calculator is for educational purposes and is not a substitute for professional medical advice.
❓ Body Surface Area Calculator FAQ
What is body surface area (BSA)?
Body surface area is the total surface area of the body, measured in square meters (m²). It's used in medicine to normalize dosing, cardiac output, and kidney function because it correlates better with metabolic mass than weight alone.
Which BSA formula is the most accurate?
There's no single "best" formula — each was derived from a different population. The Mosteller formula is the most widely used because of its simplicity. Du Bois and Haycock are considered reliable references. Comparing all five formulas (as this calculator does) gives the best overall picture.
What is a normal BSA for an adult?
Most adults have a BSA between 1.6 and 2.0 m². Taller and heavier people may be above 2.2 m²; very small adults may be below 1.4 m².
Does BSA differ between men and women?
The BSA formulas themselves do not use gender — only height and weight. However, because adult men are on average taller and heavier than adult women, average BSA values are slightly higher in men (≈1.9 m²) than in women (≈1.6 m²).
Why do different BSA formulas give different results?
Each formula was derived from a different population sample (different ages, ethnicities, and body compositions) using different regression techniques. The differences between formulas are usually small (typically under 5%) for average-sized adults, but can widen for very small children or extremely heavy adults.
How is BSA used in chemotherapy?
Many chemotherapy drugs are dosed in milligrams per square meter of BSA (mg/m²). Oncologists multiply the prescribed dose (mg/m²) by the patient's BSA to get the total dose. Mosteller is commonly used for this purpose, but some protocols specify a different formula.
Can BSA be used for weight loss or fitness tracking?
BSA is not a common fitness metric — body fat percentage, BMI, and waist circumference are better suited for tracking body composition changes. BSA is primarily a medical and clinical measurement.
Is BSA used for children?
Yes — BSA is heavily used in pediatrics for drug dosing (including chemotherapy and anesthesia). The Haycock formula is particularly well-validated in children and is often preferred for pediatric BSA.
What is the difference between BSA and BMI?
BMI (body mass index) is a ratio of weight to height² that categorizes body size. BSA measures the actual surface area of the body. BMI is used for population screening of obesity; BSA is used for clinical dosing and physiological normalization.
Why do I get different values when I use different formulas?
The formulas were derived from different populations using different regression techniques. For most adults, differences are under 5%. The average of all five formulas is the most robust estimate — which is why this calculator highlights it.
Which formula should I choose as my primary?
For clinical purposes, follow your institution's protocol. For general reference, the Mosteller formula is the most common and easiest to remember. The "Average" option (default) gives you the most representative value.
How do I convert measurements between metric and imperial?
This calculator automatically converts between metric and imperial units. Simply select your preferred unit system, enter your measurements, and the calculator handles the conversions for you.