Body Surface Area Calculator
Estimate BSA in square meters (m²) using common medical formulas.
What is body surface area (BSA)?
Body Surface Area (BSA) is an estimate of the total external area of the human body. In medicine, BSA is commonly used to scale certain clinical values more appropriately than body weight alone. The final result is usually expressed in square meters (m²).
Unlike BMI, which is a population-level screening metric for body size categories, BSA is often used for dosing and physiologic indexing. For example, some chemotherapy regimens and cardiac measurements are adjusted based on BSA.
Why BSA calculation matters
- Drug dosing: Several medications, especially in oncology, are prescribed as mg/m².
- Kidney and cardiac interpretation: Clinical values can be normalized to BSA for fair comparison across body sizes.
- Burn management: Estimating burned skin area often involves BSA concepts.
- Pediatrics: In children, body-size scaling can be especially important for safe dosing.
Common BSA formulas used in practice
There is no single universal equation. Different formulas can produce slightly different results. In most healthy adults, differences are usually modest.
| Formula | Equation (H in cm, W in kg) | Notes |
|---|---|---|
| Mosteller | BSA = √((H × W) / 3600) | Simple and very common in clinical calculators. |
| Du Bois & Du Bois | BSA = 0.007184 × H0.725 × W0.425 | Classic historical formula. |
| Haycock | BSA = 0.024265 × H0.3964 × W0.5378 | Often cited for pediatric use as well. |
| Gehan & George | BSA = 0.0235 × H0.42246 × W0.51456 | Alternative fit from measured body data. |
| Boyd | BSA = 0.0003207 × H0.3 × W(g)(0.7285 − 0.0188 × log10(W(g))) | Uses weight in grams in the exponent term. |
How to calculate BSA step by step
Metric example (Mosteller)
Suppose height = 175 cm and weight = 70 kg:
- Multiply height and weight: 175 × 70 = 12,250
- Divide by 3600: 12,250 / 3600 = 3.4028
- Square root: √3.4028 = 1.845
Estimated BSA ≈ 1.85 m²
Imperial example
For imperial units, convert first:
- Height in inches × 2.54 = cm
- Weight in pounds × 0.45359237 = kg
Then apply your selected BSA equation. The calculator above handles conversion automatically.
Interpreting your BSA result
Adult BSA often falls roughly between 1.4 and 2.2 m², though individual values can fall outside this range. A larger BSA does not automatically mean “healthier” or “less healthy”; it is primarily a size-normalization tool.
Limitations of BSA formulas
- All formulas are statistical estimates, not direct measurements of skin area.
- Differences between equations may matter in edge cases (very small or very large body size).
- Body composition is not fully captured (muscle vs fat distribution).
- Clinical context matters more than any single calculator output.
Quick FAQ
Is BSA the same as BMI?
No. BMI is weight relative to height squared and is used for population screening. BSA estimates external body area and is often used for dosing and physiologic indexing.
Which formula should I choose?
Mosteller is usually the practical default. If your clinical protocol specifies another equation (e.g., Du Bois or Haycock), follow that protocol.
Can I use BSA for self-medicating doses?
No. Never self-adjust prescription dosing from online tools. Always consult your clinician or pharmacist.