Body Surface Area Calculator
This Body Surface Area (BSA) calculator estimates the total surface area of the human body using medically validated formulas (Du Bois, Mosteller, Haycock). It is used for determining chemotherapy dosages, cardiac index, and pediatric medication scaling.
Last Updated: January 2026
Results — Body Surface Area
Why Use a BSA Calculator?
In medical practice, a "one-size-fits-all" dose rarely exists. While simple body weight is often used for dosing common medications (like antibiotics), it doesn't always reflect a patient's true metabolic mass.
Body Surface Area (BSA) is considered a more precise metric because it is less affected by abnormal fat mass. For example, two people might weigh the same, but if one is short and obese while the other is tall and muscular, their metabolic rates and blood volumes will differ. BSA accounts for this 2D surface relationship, making it the gold standard for drugs with a "narrow therapeutic index" where the difference between a cure and toxicity is small.
Primary Clinical Use Cases
- Oncology: Calculating chemotherapy and immunotherapy dosages (mg/m²).
- Cardiology: determining Cardiac Index (CI) to assess heart pump function relative to body size.
- Nephrology: Adjusting Glomerular Filtration Rate (GFR) to assess kidney function.
- Pediatrics: Prescribing corticosteroids and fluid replacement therapy for children.
Supported BSA Formulas
Medical institutions may prefer different formulas based on the patient's age or the specific treatment protocol. This tool calculates the following standard equations simultaneously:
1. The Mosteller Formula (Most Common)
BSA = √ ( (Height(cm) × Weight(kg)) / 3600 )
Widely adopted for its mathematical simplicity and verified accuracy. It is the default for many clinical trials and hospital protocols today.
2. The Du Bois & Du Bois Formula (Historical Standard)
BSA = 0.007184 × Weight(kg)^0.425 × Height(cm)^0.725
The classic benchmark developed in 1916. While highly accurate for standard body types, some modern data suggests it may underestimate BSA in obese patients compared to Mosteller.
3. The Haycock Formula (Pediatric)
BSA = 0.024265 × Weight(kg)^0.5378 × Height(cm)^0.3964
Specifically validated for infants and children. It is often preferred in Neonatal Intensive Care Units (NICU) as it maintains accuracy even at very low surface areas.
4. Boyd, Gehan & George
These variations offer alternative statistical coefficients. The Boyd formula, for instance, uses a variable exponent for weight, allowing it to self-adjust for extremes in body mass, though it is computationally more complex.
How BSA Differs from BMI
It is common to confuse Body Surface Area (BSA) with Body Mass Index (BMI), but they measure fundamentally different things.
| Feature | Body Surface Area (BSA) | Body Mass Index (BMI) |
|---|---|---|
| Definition | Total surface area of the skin (m²). | Ratio of weight to height squared (kg/m²). |
| Medical Focus | Metabolism, blood volume, drug clearance. | Obesity classification, cardiovascular risk. |
| Athletes | Accurate scaling for muscle mass. | Often misclassifies muscular people as "overweight". |
Accuracy and Limitations
While BSA is a critical tool, it relies on the accuracy of the height and weight inputs.
- Amputations: Standard formulas assume a complete body. For patients with amputations, the estimated surface area of the missing limb must be subtracted from the total.
- Morbid Obesity: In very obese patients, BSA formulas can overestimate the "metabolically active" area. To prevent toxicity, oncologists often "cap" the BSA calculation (commonly at 2.0 m² or 2.2 m²) regardless of the actual mathematical result.
- Fluid Status: Weight should ideally be measured "dry" (before IV fluids) to prevent water weight from skewing the calculation.
Frequently Asked Questions
Disclaimer
This Body Surface Area (BSA) tool is provided for educational and informational purposes only.
Medical Warning: Do not rely on this tool for professional medical diagnosis or treatment. Chemotherapy and medication dosing must always be verified by a qualified healthcare provider using institutional protocols. Calculatorbudy assumes no liability for clinical decisions based on these results.