BSA Calculator - Body Surface Area
Estimate your bsacalculator body surface area with our free body measurements calculator. See reference ranges, risk factors, and next-step guidance.
Reviewed by Rahul Singh, Health & Wellness Specialist
Formula
Du Bois: BSA = 0.007184 x W^0.425 x H^0.725
Where W is weight in kilograms and H is height in centimeters. The Du Bois formula (1916) is the most widely used. Alternative formulas include Mosteller (sqrt(H x W / 3600)), Haycock (0.024265 x W^0.5378 x H^0.3964), Boyd, and Gehan-George, each with slightly different coefficients optimized for different populations.
Worked Examples
Example 1: Standard Adult BSA Calculation
Problem:Calculate BSA for an adult weighing 70 kg and 175 cm tall using the Du Bois formula.
Solution:Du Bois: BSA = 0.007184 x 70^0.425 x 175^0.725\n70^0.425 = 6.08\n175^0.725 = 42.30\nBSA = 0.007184 x 6.08 x 42.30 = 1.849 m^2\n\nMosteller: BSA = sqrt(175 x 70 / 3600) = sqrt(3.403) = 1.844 m^2\nAverage adult reference BSA = 1.73 m^2\nThis patient BSA is 6.9% above average
Result:BSA: 1.85 m^2 (Du Bois) | 1.84 m^2 (Mosteller) | Above average
Example 2: Pediatric BSA for Drug Dosing
Problem:A child weighs 25 kg and is 120 cm tall. Calculate BSA using the Haycock formula for chemotherapy dosing.
Solution:Haycock: BSA = 0.024265 x 25^0.5378 x 120^0.3964\n25^0.5378 = 5.65\n120^0.3964 = 6.67\nBSA = 0.024265 x 5.65 x 6.67 = 0.914 m^2\nCompared to average adult 1.73 m^2: 52.8%\nDrug dose would be scaled accordingly
Result:BSA: 0.93 m^2 (Haycock) | 53% of adult average | Pediatric dosing required
Frequently Asked Questions
What is Body Surface Area (BSA) and why is it important?
Body Surface Area is a measurement of the total external surface of the human body, expressed in square meters. BSA is clinically important because many physiological processes scale more accurately with body surface area than with body weight alone. Drug dosing in oncology is almost exclusively based on BSA because the rate of drug metabolism and clearance correlates better with surface area than with weight. BSA is also used to calculate cardiac index (cardiac output divided by BSA), renal function indices, and burn area assessment. For chemotherapy agents, using BSA-based dosing helps standardize drug exposure across patients of different sizes, reducing the risk of underdosing in large patients or overdosing in small patients.
Which BSA formula should I use?
The choice of BSA formula depends on the clinical context and patient population. The Du Bois formula (1916) is the most historically established and widely referenced in medical literature, making it the default choice for most clinical applications. The Mosteller formula is popular in oncology practice because of its simplicity, requiring only a square root calculation. The Haycock formula is preferred in pediatric settings because it was validated using data from children and infants. The Gehan and George formula offers good accuracy across a wide range of body sizes. For routine clinical use, the differences between formulas are typically small (less than 5 percent), so consistency in formula choice within a practice is more important than which formula is selected.
How does the Du Bois BSA formula work?
The Du Bois formula, published in 1916 by Delafield Du Bois and Eugene Du Bois, calculates BSA as 0.007184 multiplied by weight in kilograms raised to the power of 0.425, multiplied by height in centimeters raised to the power of 0.725. The formula was derived from direct surface area measurements of nine individuals whose bodies were coated with thin paper and the paper area calculated. Despite the small sample size, the formula has proven remarkably accurate across diverse populations over more than a century of clinical use. The exponents 0.425 for weight and 0.725 for height were determined through regression analysis and reflect the allometric scaling relationship between body dimensions and surface area.
Why is BSA used for chemotherapy dosing instead of weight?
Chemotherapy dosing is based on BSA because pharmacokinetic studies have shown that drug clearance rates and toxicity profiles correlate more consistently with body surface area than with total body weight. This is because BSA better reflects metabolically active tissue mass, blood volume, and organ size than weight alone. Two patients of the same weight but different heights will have different BSA values and may require different drug doses. BSA-based dosing became standard in oncology in the 1950s and 1960s when early chemotherapy trials demonstrated that fixed doses caused unacceptable toxicity variation across patients of different sizes. While some researchers have questioned whether BSA is truly optimal for all drugs, it remains the standard of care for most chemotherapy protocols.
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy