Enter Your Measurements
Your Body Surface Area (Du Bois)
Used for medical calculations and drug dosing
BSA Formula Comparison
| Formula | BSA (m2) | Year | Notes |
|---|---|---|---|
| Du BoisMost Common | 0.00 | 1916 | Most widely used in clinical practice |
| MostellerSimplest | 0.00 | 1987 | Easiest to calculate, clinically practical |
| Haycock | 0.00 | 1978 | Preferred for children |
| Gehan & George | 0.00 | 1970 | Accurate across wide range of ages |
| Boyd | 0.00 | 1935 | Complex formula, high precision |
BSA Relative to Average Adult (1.7 m2)
Newborn 1.0 m2
Child 1.7 m2
Average 2.5 m2
Large Adult
Reference Ranges
Adult Male
Adult Female
Child (10 years)
Newborn
Clinical Applications of BSA
Drug Dosing
BSA is used to calculate dosages for chemotherapy agents, immunosuppressants, and other medications with narrow therapeutic windows. It provides more accurate dosing than body weight alone.
Burn Assessment
The "Rule of Nines" uses BSA to assess burn severity. Calculating the percentage of BSA affected helps determine fluid resuscitation needs and prognosis.
Cardiac Index
Cardiac output is normalized by BSA to calculate cardiac index (L/min/m2), allowing comparison across patients of different body sizes. Normal cardiac index is 2.5-4.0 L/min/m2.
Renal Function
Glomerular filtration rate (GFR) is often adjusted to BSA (normalized to 1.73 m2) to standardize kidney function measurements across different body sizes.
Understanding Body Surface Area (BSA)
Body Surface Area (BSA) is the measured or calculated surface area of the human body, expressed in square meters (m2). Unlike simple height or weight measurements, BSA takes both dimensions into account, providing a more comprehensive assessment of body size that correlates better with physiological parameters like metabolic rate, blood volume, and organ size.
BSA is widely used in medicine because many physiological processes are proportional to body surface area rather than body weight. For example, heat loss, metabolic rate, and drug metabolism all correlate more closely with BSA than with weight alone. This makes BSA particularly valuable for calculating drug dosages, especially for medications with narrow therapeutic windows where precision is critical.
BSA Calculation Formulas
Du Bois Formula (1916) - Most Common
The Du Bois formula is the most widely cited BSA equation in medical literature. Published in 1916, it has been validated across numerous studies and remains the standard for clinical practice. It was derived from measurements of nine subjects using a coating method to determine actual surface area.
Mosteller Formula (1987) - Simplest
The Mosteller formula is considered the simplest and most clinically practical BSA calculation. It provides results very similar to the Du Bois formula but is much easier to calculate manually. Many clinicians prefer this formula for bedside calculations.
Haycock Formula (1978)
The Haycock formula is often preferred for calculating BSA in children. It was derived from measurements in infants and children and tends to be more accurate for pediatric populations.
Gehan & George Formula (1970)
This formula was developed from a large dataset spanning a wide range of ages and body sizes, making it accurate across diverse populations.
Boyd Formula (1935)
The Boyd formula is more complex but can provide high precision. It uses weight in grams rather than kilograms. This formula is less commonly used in clinical practice due to its complexity.
Why BSA Matters in Medicine
Correlation with Physiology: BSA correlates more closely than body weight with important physiological parameters including cardiac output, blood volume, metabolic rate, and renal function. A person's metabolic rate is roughly proportional to their surface area because heat loss occurs through the skin.
Drug Dosing: Many medications, particularly chemotherapy agents, are dosed based on BSA rather than body weight. Two people with the same weight but different heights have different metabolic rates and organ sizes. BSA-based dosing accounts for these differences, providing more consistent drug levels and therapeutic effects across patients of varying body compositions.
Standardization: BSA allows medical measurements to be standardized and compared across patients. For example, cardiac index (cardiac output per BSA) and GFR adjusted for BSA enable meaningful comparisons between a small woman and a large man.
Limitations of BSA
While BSA is useful, it has limitations. The formulas assume normal body proportions and may be less accurate for individuals with extreme obesity, very muscular builds, or unusual body proportions. Additionally, different formulas can give results that vary by up to 10%, though in most cases the differences are smaller (typically 2-5%).
For extremely obese patients, some clinicians use adjusted body weight calculations in addition to or instead of BSA. For children, pediatric-specific formulas like Haycock may be more appropriate. Always consult with a healthcare provider for medical applications of BSA calculations.
Frequently Asked Questions
Privacy & Limitations
- All calculations run entirely in your browser -- nothing is sent to any server.
- Results are estimates and should not replace professional medical advice.
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Body Surface Area Calculator FAQ
What is body surface area (BSA)?
Body Surface Area (BSA) is the total area of the outer surface of the human body, measured in square meters (m2). The average adult BSA is approximately 1.7 m2. BSA is used in medicine to calculate drug dosages, assess burn injuries, determine cardiac output, and adjust renal function measurements.
What is the Du Bois formula for BSA?
The Du Bois formula, published in 1916, is: BSA = 0.007184 x Height(cm)^0.725 x Weight(kg)^0.425. It is the most widely used BSA formula in clinical practice and medical literature.
Why is BSA used instead of body weight for drug dosing?
BSA correlates better with metabolic rate and organ size than body weight alone. Two people of the same weight but different heights have different metabolic rates. BSA-based dosing provides more consistent drug levels across patients of different body compositions, which is especially important for drugs with narrow therapeutic windows like chemotherapy agents.
What is normal BSA for adults?
Average BSA for adult males is approximately 1.9 m2 (range 1.5-2.2 m2) and for adult females approximately 1.6 m2 (range 1.3-1.9 m2). Newborns have a BSA of about 0.25 m2. BSA varies significantly based on height and weight.
Which BSA formula is most accurate?
The Mosteller formula is considered the simplest and clinically practical choice: BSA = sqrt(height(cm) x weight(kg) / 3600). The Du Bois formula is the most widely cited. For obese patients, Mosteller may be slightly more accurate. For children, the Haycock formula is often preferred. In practice, the differences between formulas are usually small (within 5%).