Body Surface Area (BSA) Calculator
| Formula | BSA (m²) |
|---|---|
| Du Bois (1916) | — |
| Mosteller (1987) | — |
| Haycock (1978) | — |
| Boyd (1935) | — |
Average BSA (across formulas)
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Interpretation
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How Body Surface Area Is Used in Medicine
Body Surface Area (BSA) is a clinical measurement that estimates the total area of the human body's outer surface, expressed in square meters (m2). According to the National Library of Medicine, BSA is a more proportional indicator of metabolic mass than body weight alone because it accounts for both height and weight. The average adult BSA is approximately 1.7 m2 for women and 1.9 m2 for men.
BSA is critically important in oncology for calculating chemotherapy drug dosages, where precise dosing determines the balance between therapeutic efficacy and toxicity. The National Cancer Institute notes that most chemotherapy protocols use BSA-based dosing. BSA is also used to compute the cardiac index (cardiac output / BSA), estimate glomerular filtration rate (GFR) for kidney function, and calculate fluid resuscitation requirements in burn patients. Use our BMI Calculator for general body composition assessment, or the Creatinine Clearance Calculator for kidney function estimates that use BSA normalization.
BSA Formulas Explained
Several formulas have been developed to estimate BSA from height and weight. Each has different origins and strengths. This calculator presents four formulas simultaneously for comparison.
Du Bois (1916): BSA = 0.007184 x Height(cm)^0.725 x Weight(kg)^0.425
The historical standard, validated against direct surface measurements of 9 subjects.
Mosteller (1987): BSA = sqrt(Height(cm) x Weight(kg) / 3600)
The simplest formula; widely used in clinical practice for its ease of calculation.
Haycock (1978): BSA = 0.024265 x Height(cm)^0.3964 x Weight(kg)^0.5378
Developed from pediatric data; preferred for children and infants.
Boyd (1935): BSA = 0.0003207 x Height(cm)^0.3 x Weight(g)^(0.7285 - 0.0188 x log10(Weight(g)))
Places greater emphasis on weight; may diverge from other formulas in obese patients.
Worked example: A 170 cm, 70 kg adult: Du Bois = 1.81 m2, Mosteller = 1.81 m2, Haycock = 1.81 m2, Boyd = 1.80 m2. For average-sized adults, all formulas converge closely.
Key BSA Terms You Should Know
- Body Surface Area (BSA): The estimated total outer surface area of the human body in m2. Used as a dosing parameter for drugs with narrow therapeutic indices.
- Cardiac Index (CI): Cardiac output divided by BSA (normal: 2.5-4.0 L/min/m2). Normalizes cardiac output for body size to enable comparison between patients.
- BSA-normalized GFR: Kidney filtration rate adjusted to a standard BSA of 1.73 m2, enabling comparison across patients of different sizes.
- Therapeutic Window: The range of drug concentrations between the minimum effective dose and the toxic dose. BSA-based dosing helps keep drugs within this window.
- Chemotherapy Dosing: Drug dose (mg) = BSA (m2) x protocol dose (mg/m2). For example, if a protocol calls for 75 mg/m2 and the patient's BSA is 1.8 m2, the dose is 135 mg.
BSA Formula Comparison
The following table compares BSA values across the four formulas for different body sizes, illustrating when results converge and diverge. Data based on calculations from the formulas published in the Journal of Oncology Pharmacy Practice.
| Height / Weight | Du Bois | Mosteller | Haycock | Boyd |
|---|---|---|---|---|
| 150 cm / 50 kg | 1.43 m2 | 1.44 m2 | 1.44 m2 | 1.42 m2 |
| 170 cm / 70 kg | 1.81 m2 | 1.81 m2 | 1.81 m2 | 1.80 m2 |
| 180 cm / 90 kg | 2.10 m2 | 2.12 m2 | 2.12 m2 | 2.09 m2 |
| 175 cm / 120 kg | 2.33 m2 | 2.42 m2 | 2.40 m2 | 2.29 m2 |
| 80 cm / 10 kg (child) | 0.46 m2 | 0.47 m2 | 0.47 m2 | 0.47 m2 |
Practical Examples
Example 1 - Chemotherapy dosing: A 165 cm, 65 kg woman with BSA of 1.72 m2 is prescribed carboplatin at 300 mg/m2. Her dose: 1.72 x 300 = 516 mg. Accurate BSA calculation is critical because carboplatin has a narrow therapeutic window.
Example 2 - Cardiac assessment: A patient with cardiac output of 5.0 L/min and BSA of 1.85 m2 has a Cardiac Index of 5.0 / 1.85 = 2.7 L/min/m2, which is within the normal range (2.5-4.0). Without BSA normalization, comparing cardiac output between a 55 kg woman and a 95 kg man would be misleading.
Example 3 - Pediatric dosing: A 12 kg, 80 cm toddler has a BSA of approximately 0.47 m2 using the Haycock formula (preferred for children). For a drug dosed at 150 mg/m2: 0.47 x 150 = 70.5 mg. Pediatric dosing requires the most precise BSA calculation. Track the child's growth over time with our Baby Growth Calculator.
Tips for Using BSA Calculations
- Choose the right formula for the patient: Use Haycock for pediatric patients, Mosteller for general clinical use due to its simplicity, and Du Bois as the default when protocol does not specify. Most institutions have a preferred formula.
- Account for obesity carefully: BSA formulas diverge most for obese patients. Some oncology protocols cap BSA at 2.0 m2 or use adjusted body weight to avoid toxicity from overdosing.
- Never self-dose medications based on BSA: BSA-based drug dosing should only be performed by trained healthcare professionals. Slight calculation errors with chemotherapy agents can have serious consequences.
- Use actual height and weight: Measured values are more accurate than self-reported. A 5 cm height error can change BSA by 0.05-0.1 m2, which may matter for narrow-window drugs.
- Compare with body fat percentage: BSA does not distinguish between lean mass and fat mass. Two patients with the same BSA but different body compositions may metabolize drugs differently.
BSA in Clinical Research
According to a meta-analysis in the Journal of Oncology Pharmacy Practice, the Mosteller and Du Bois formulas agree within 0.5% for average-sized adults but can diverge by 3-5% for obese patients. The average adult male BSA in the United States is approximately 1.94 m2, and the average adult female BSA is 1.69 m2. BSA-based drug dosing has been the standard in oncology since the 1950s, though some researchers have argued for fixed dosing for certain drugs. The Du Bois formula, despite being based on only 9 subjects in 1916, has remained remarkably accurate when validated against modern 3D body scanning technology.
Frequently Asked Questions
What is Body Surface Area (BSA)?
Body Surface Area is a measurement of the total outer surface area of the human body, expressed in square meters (m2). The average adult BSA is approximately 1.7 m2 for women and 1.9 m2 for men. BSA is used in medicine to calculate chemotherapy dosages, determine cardiac index (cardiac output divided by BSA), estimate GFR for kidney function, and adjust other clinical measurements that depend on body size. Unlike weight alone, BSA provides a more proportional indicator of metabolic mass.
What is the Du Bois formula for BSA?
The Du Bois formula, published in 1916, is one of the most widely used BSA formulas: BSA = 0.007184 x Height(cm)^0.725 x Weight(kg)^0.425. Despite being developed from measurements of only 9 subjects over a century ago, it has been validated by modern 3D body scanning and remains a standard in clinical practice. It may slightly underestimate BSA in obese individuals compared to the Mosteller formula.
Which BSA formula is most accurate?
No single formula is universally most accurate. The Mosteller formula is popular for its simplicity and is widely used in clinical practice. The Haycock formula is preferred for pediatric patients because it was developed using measurements from children. The Du Bois formula is the historical standard. All formulas agree closely (within 0.5%) for average-sized adults but can diverge by 3-5% for obese or pediatric patients. Most institutions specify which formula to use in their protocols.
Why is BSA used instead of body weight for drug dosing?
BSA correlates better than body weight alone with many physiological processes including cardiac output, blood volume, renal function, and metabolic rate. Drug clearance and distribution often scale more proportionally with BSA. This is especially important for drugs with narrow therapeutic windows, such as chemotherapy agents, where the difference between an effective and toxic dose may be small. A 2015 review in the journal Clinical Pharmacokinetics confirmed that BSA-based dosing reduces inter-patient variability in drug exposure compared to flat dosing for most cytotoxic agents.
How does obesity affect BSA calculations?
Obesity causes BSA formulas to diverge more significantly. The Mosteller formula tends to give slightly higher values for obese patients than Du Bois. Some oncology protocols cap BSA at 2.0 m2 or use adjusted body weight (ideal body weight + 0.4 x excess weight) to avoid potential toxicity from high doses. The decision to cap or adjust is drug-specific and should be made by the treating physician. Use our Ideal Weight Calculator to determine adjusted body weight when needed.