Du Bois (1916)
Original formula
1.85m²
Scenario
BSA vs BMI — When Body Surface Area Matters More
Understand the differences between BSA and BMI. Learn when BSA provides more clinically useful information than BMI.
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Your Details
cm
kg
Your BSA Results
Mosteller (1987)
Most common
1.84m²
Haycock (1978)
Pediatric use
1.85m²
m²
Average of all three formulas
BSA on Reference Scale
1.85 m²
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- 2.5
Formula Comparison
BSA Reference Range: Average BSA is approximately 1.7 m² for men and 1.6 m² for women. Your average BSA of 1.85 m² is above average, which is common for taller or larger-framed individuals.
The formula
The formula
What BSA Measures
Body Surface Area (BSA) is a measurement of the total external surface area of the human body, expressed in square meters (m²). Unlike BMI, which assesses weight relative to height, BSA estimates the physical extent of the body surface — a metric that correlates closely with metabolic rate, blood volume, and cardiac output.
BSA is most commonly used in clinical medicine to calculate chemotherapy dosages, determine medication doses for drugs with narrow therapeutic windows, and normalize physiological indices such as cardiac index and glomerular filtration rate. Because BSA-based dosing scales drug delivery to a patient's size more precisely than weight alone, it is the standard of care in oncology and several other specialties.
The BSA Formulas
Three validated formulas are provided in this calculator. Each was derived from measurements of different populations, and while they produce similar results for most adults, minor differences are expected. The most widely used formula in current clinical practice is the Mosteller formula, valued for its simplicity.
Du Bois (1916)
BSA = 0.007184 × W0.425 × H0.725
Mosteller (1987)
BSA = √(W × H ÷ 3600)
Haycock (1978)
BSA = 0.024265 × W0.5378 × H0.3964
Where W = weight in kilograms, H = height in centimeters
Formula Source
Du Bois & Du Bois (1916) — A formula to estimate the approximate surface area if height and weight be known. Archives of Internal Medicine, 17, 863–871.
Reference URL: https://doi.org/10.1001/archinte.1916.00080130008002
Mosteller (1987) — Simplified calculation of body-surface area. New England Journal of Medicine, 317(17), 1098.
Reference URL: https://doi.org/10.1056/NEJM198707233170417
Haycock et al. (1978) — Geometric method for measuring body surface area: A height-weight formula validated in infants, children, and adults. The Journal of Pediatrics, 93(1), 62–66.
Last Verified: 2026-08-09
Worked Example
Consider an adult who weighs 70 kg and stands 175 cm tall. Applying each formula side by side:
Du Bois: 0.007184 × 700.425 × 1750.725 = 0.007184 × 6.08 × 42.29 ≈ 1.85 m²
Mosteller: √(70 × 175 ÷ 3600) = √(12,250 ÷ 3600) = √3.403 ≈ 1.84 m²
Haycock: 0.024265 × 700.5378 × 1750.3964 = 0.024265 × 9.82 × 7.75 ≈ 1.85 m²
All three formulas converge near 1.85 m² for this individual, which is a typical adult BSA value. The small variation between formulas (within 0.01 m² in this case) is clinically acceptable for most applications.
BSA Formula Comparison Table
| Formula | Equation | Typical Use Case |
|---|---|---|
| Du Bois (1916) | 0.007184 × W0.425 × H0.725 | Original reference standard; widely cited in research and historical clinical data. |
| Mosteller (1987) | √(W × H ÷ 3600) | Most commonly used in modern clinical practice due to its simplicity and strong agreement with the Du Bois formula. |
| Haycock (1978) | 0.024265 × W0.5378 × H0.3964 | Often preferred for pediatric and neonatal populations; validated across a wider age range including infants. |
Why BSA Alone Is Not a Full Picture
BSA is a powerful clinical tool, but it is not a standalone health assessment. A single BSA value does not reveal whether a person is underweight, overweight, or has a healthy body composition. Two individuals with identical BSA can have very different ratios of muscle to fat, different metabolic rates, and different overall health profiles.
BSA is most useful when applied as part of a broader clinical context — for example, when calculating a chemotherapy dose, the clinician also considers organ function, performance status, and prior treatment response. For general wellness tracking, BSA is less informative than BMI, waist circumference, or body composition measurements.
Known Limitations
- BSA formulas are population-derived estimates, not direct measurements. Actual surface area varies with body shape, posture, and individual anatomy.
- The Du Bois formula was derived from only nine subjects, which limits its statistical generalizability across diverse populations.
- BSA formulas may be less accurate at extremes of height and weight (very tall, very short, underweight, or severely obese individuals).
- BSA does not account for body composition — two people with the same BSA can have very different fat-to-muscle ratios.
- BSA is not a fitness metric. It was designed for medical dosing and physiological normalization, not for tracking weight or health status over time.
Scenario guide
Scenario guide
What each measure tells you
- BMI (Body Mass Index): Weight / Height² — a simple screening tool for weight status (underweight, normal, overweight, obese). Used primarily in population health and general medicine.
- BSA (Body Surface Area): A measure of total body surface — derived from both height and weight. Used primarily for drug dosing, cardiac function assessment, and physiological parameter normalization.
When BSA matters more than BMI
- Drug dosing: Many medications (chemotherapy, some antibiotics, corticosteroids) are dosed per m² of BSA because it correlates better with drug distribution and clearance than weight or BMI
- Cardiac assessment: Cardiac output is normalized to BSA (cardiac index = CO/BSA) to compare heart function across patients of different sizes
- Renal function: eGFR (estimated glomerular filtration rate) is normalized to 1.73 m² BSA for standardized comparison
- Burn assessment: Burn severity is expressed as % of total BSA burned
- Metabolic rate estimation: Basal metabolic rate correlates better with BSA than with weight or BMI
Key differences at a glance
- BMI: 1 number (weight ÷ height²). Categorizes weight status. Does not distinguish muscle from fat.
- BSA: 1 number (derived from height and weight). Represents total body surface. Used for proportional dosing and physiological normalization.
- Overlap: Both use height and weight as inputs, but produce different numbers with different clinical meanings.
Example: Same BMI, different BSA
Patient A: 160 cm, 65 kg → BMI = 25.4, BSA ≈ 1.67 m² Patient B: 180 cm, 90 kg → BMI = 27.8, BSA ≈ 2.02 m² Both are "overweight" by BMI, but Patient B has 21% more BSA. If a drug is dosed at 100 mg/m², Patient A gets 167 mg and Patient B gets 202 mg — a 21% difference that weight or BMI alone would not capture accurately.
Bottom line
BMI is a screening tool for weight status. BSA is a clinical parameter for proportional drug dosing and physiological normalization. They serve different purposes and are not interchangeable. In clinical settings, both may be calculated and used for different decisions.
FAQ
Frequently Asked Questions
They serve different purposes. BMI screens for weight status; BSA is used for drug dosing and physiological normalization. Neither is universally "better" — they answer different clinical questions.
BSA is preferred when drug distribution correlates better with body surface than with body weight — this includes many chemotherapy agents, some antibiotics, and drugs metabolized by the liver or kidneys.
Both use height and weight as inputs, but produce different numbers with different meanings. BMI = weight/height² (weight status); BSA = √(height×weight/3600) (body surface area for dosing).
Cardiac index (cardiac output ÷ BSA) allows fair comparison of heart function across patients of different sizes. A large person naturally has a higher cardiac output than a small person, but their cardiac index may be similar.
For general health monitoring, BMI is the standard screening tool. BSA is primarily a clinical parameter used by healthcare providers for specific medical calculations, not for routine health tracking.
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