Quick answer: Body surface area (BSA) is your total skin area in m², estimated from height and weight. A typical adult BSA is 1.6 to 2.2 m² (about 1.9 for men, 1.6 for women). Doctors use BSA to dose chemotherapy, compute cardiac index, and normalize kidney function.
Last reviewed: October 2026
Key facts
- DuBois formula: BSA = 0.007184 x weight(kg)0.425 x height(cm)0.725.
- Mosteller shortcut: BSA = square root of (height(cm) x weight(kg) / 3600).
- Normal adult BSA: 1.6 - 2.2 m²; results outside this band deserve a second look.
- BSA scales drug doses (mg/m²), cardiac index, and GFR better than weight alone.
A body surface area calculator estimates your BSA from height and weight using the standard DuBois formula, with the simpler Mosteller formula as an option. Enter your measurements in metric or imperial units to get your BSA in square meters.
BSA reflects metabolic rate and drug clearance better than weight alone, which is why many chemotherapy doses are prescribed per square meter of body surface. It also underlies the cardiac index (cardiac output divided by BSA) and the normalized glomerular filtration rate used to judge kidney function. This free body surface area calculator gives you an instant answer with no signup.
How to use this body surface area calculator
- Choose your unit system: Metric (kg/cm) or Imperial (lb/in).
- Enter your weight and height.
- Pick a formula: DuBois (the clinical classic) or Mosteller (the simple shortcut).
- Click Calculate to see your body surface area in m².
Body surface area formula (DuBois)
W is weight in kilograms and H is height in centimeters. The DuBois formula dates to 1916 and remains the most widely cited clinical model. The Mosteller alternative, BSA = sqrt(H x W / 3600), usually lands within a few percent of DuBois and is easier to compute by hand.
Body surface area calculator worked examples
Metric: 70 kg at 170 cm (DuBois)
BSA = 0.007184 x 700.425 x 1700.725 = 0.007184 x 6.084 x 41.41 = 1.81 m² (rounded), squarely in the normal adult range. Mosteller gives 1.82 m², a difference under 1%.
Imperial: 154 lb at 5 ft 7 in (DuBois)
Convert first: 154 lb = 69.85 kg, 67 in = 170.18 cm. BSA = 0.007184 x 69.850.425 x 170.180.725 = 1.81 m² (rounded), the same body measured in different units.
Typical BSA reference values
| Group | Typical BSA (m²) |
|---|---|
| Adult men | ~1.9 (range 1.7 - 2.1) |
| Adult women | ~1.6 (range 1.4 - 1.8) |
| Children, 12 - 14 years | ~1.33 |
| Children, 9 - 10 years | 1.07 - 1.14 |
Body surface area calculator tips for accurate results
Enter morning measurements: weight is most stable before breakfast, and height is slightly taller in the morning than the evening. Use metric units when you can: the DuBois formula is defined in kilograms and centimeters, so imperial entries add a conversion step. Pick one formula and stick with it for tracking: DuBois and Mosteller agree within a few percent, but switching between them adds noise to your trend. And never dose medication from the number alone: chemotherapy and other mg/m2 drugs are prescribed by a clinician, and this body surface area calculator is an estimate, not a prescription.
Frequently asked questions
What is body surface area used for?
BSA scales medication doses (many chemotherapy drugs are dosed in mg per m²), cardiac index, and normalized kidney function (GFR). It tracks metabolic rate and drug clearance better than body weight alone.
Which BSA formula is most accurate?
No single formula is proven most accurate since BSA cannot be measured directly in living people. Mosteller is the most common in clinical practice because it is simple and reliable; DuBois is the oldest validated model; Haycock is often preferred for children. They usually agree within about 5%.
What is a normal BSA for adults?
Typical adult BSA runs about 1.6 to 2.2 m²: roughly 1.9 m² for men and 1.6 m² for women. Children are much lower, from around 0.5 m² for infants up toward adult values in the teens.
Can I use BSA to estimate calorie needs?
Roughly. Maintenance calories run about 1,500 - 1,800 kcal per m² of BSA per day. But for practical nutrition planning, formulas like Mifflin-St Jeor (used in BMR and calorie calculators) are more direct.
Why does chemotherapy dosing use BSA?
Many cancer drugs have a narrow window between an effective dose and a toxic one. BSA-based dosing (mg/m²) keeps blood drug levels steadier across patient sizes than weight-only dosing, balancing efficacy against toxicity.
Can this calculator be used for children?
The math works for any body size, and pediatric teams commonly use Mosteller or Haycock. But medication doses for children must come from a clinician or institutional protocol, never from a general calculator alone.
Is BSA the same as BMI?
No. BMI divides weight by height squared to screen for weight categories, while BSA estimates total skin area to scale drug doses and physiological measures. Two people with the same BMI can have different BSA values if their heights differ. BMI is a population screening tool; BSA is a clinical sizing tool.
Why do Mosteller and Du Bois give slightly different answers?
They are different curve fits to the same body measurements, so small differences are normal. For a 170 cm, 70 kg adult, Mosteller gives 1.82 m² and Du Bois gives 1.81 m², a difference of about 0.5%. The formulas agree within about 5% for most adults but can diverge more at the extremes of size, which is why a chemotherapy protocol names the exact formula to use rather than letting each clinician pick one.
What does the 1.73 m² figure in kidney test results mean?
Kidney function (eGFR) is reported per 1.73 m², the standard reference adult body surface area, so results are comparable between people of different sizes. It does not mean your BSA is 1.73 m²: if your BSA is 2.00 m², your absolute filtration rate is higher than the normalized figure suggests, and a clinician adjusts for that when it matters.
Sources
- PMC / Indian Journal of Pharmacology: BSA-based drug dosage; Mosteller and DuBois formulas
Key takeaways
- Bookmark this body surface area calculator for quick recalculations whenever your inputs change.
- DuBois: BSA = 0.007184 x weight(kg)^0.425 x height(cm)^0.725.
- Mosteller shortcut: BSA = sqrt(height x weight / 3600), within ~5% of DuBois.
- Normal adult BSA is about 1.6 to 2.2 m².
- BSA doses chemotherapy and scales cardiac index and GFR better than weight alone.
Comments
Leave a comment