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.
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Formula
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.
Last reviewed: January 2026
Worked Examples
Example 1: Standard Adult BSA Calculation
Example 2: Pediatric BSA for Drug Dosing
Background & Theory
The BSA Calculator - Body Surface Area applies the following established principles and formulas. Clinical medicine relies on standardized measurement tools and formulas to guide diagnosis, dosing, and patient monitoring with precision and reproducibility. Pediatric and weight-sensitive drug dosing is calculated in milligrams per kilogram of body weight, a method that adjusts for physiological variation across patient sizes and ensures therapeutic drug levels without toxicity. This principle extends to adult populations for medications with narrow therapeutic indices, such as aminoglycosides and anticoagulants. Glomerular filtration rate, or GFR, is the primary index of kidney function, estimating how much blood the kidneys filter per minute. The CKD-EPI equation, developed in 2009 and refined in 2021 to remove the race variable, uses serum creatinine, age, and sex to estimate GFR, classifying chronic kidney disease stages from G1 (above 90 mL/min/1.73m²) through G5 (below 15 mL/min/1.73m²). The older Cockcroft-Gault formula remains valuable for calculating creatinine clearance to guide drug dosing. Body surface area is critical for chemotherapy dosing and certain cardiovascular assessments. The Mosteller formula, BSA = square root of (height in cm × weight in kg / 3600), is favored for its computational simplicity and clinical accuracy. Du Bois, Haycock, and Gehan-George formulas are alternatives used in specific pediatric and research settings. Fluid balance calculations track intake against output to guide intravenous therapy, particularly in critical care, surgery recovery, and burn management. The Parkland formula calculates initial fluid resuscitation for burns as 4 mL × weight in kg × percent body surface area burned, delivered over 24 hours. The Glasgow Coma Scale, scored across eye opening, verbal response, and motor response, provides a standardized neurological assessment with scores ranging from 3 (deep coma) to 15 (fully alert). The APGAR score, assessed at one and five minutes after birth across five criteria, quantifies neonatal transition to extrauterine life. Both scales support rapid clinical decision-making and interoperability across care teams.
History
The history behind the BSA Calculator - Body Surface Area traces back through the following developments. Clinical measurement as a formal discipline emerged from centuries of empirical observation systematized into reproducible tools. The measurement of body temperature became practical following Daniel Gabriel Fahrenheit's development of the mercury thermometer in 1714, which established a calibrated temperature scale. Anders Celsius introduced the centigrade scale in 1742, and Carl Wunderlich's 19th-century hospital surveys of over a million temperature readings established the normal range of 36 to 37.5 degrees Celsius, giving thermometry a clinical reference standard. Blood pressure measurement was transformed by Scipione Riva-Rocci's invention of the arm-cuff sphygmomanometer in 1896, which allowed non-invasive systolic pressure measurement. Nikolai Korotkoff's 1905 description of auscultatory sounds during cuff deflation enabled both systolic and diastolic readings, creating the method still in standard clinical use today. Willem Einthoven's invention of the electrocardiograph in 1901 and his receipt of the Nobel Prize in 1924 formalized cardiac electrical measurement and initiated a century of electrophysiological diagnostics. The first rigorous controlled clinical trial in modern medicine is credited to Austin Bradford Hill and the Medical Research Council streptomycin tuberculosis trial of 1948, which introduced randomization, control groups, and blinding as methodological cornerstones. Hill subsequently developed the criteria for causal inference in epidemiology, shaping how clinical evidence is generated and interpreted. The Glasgow Coma Scale was developed by Graham Teasdale and Bryan Jennett at the University of Glasgow in 1974 as a standardized neurological assessment for trauma patients. The APGAR score was introduced by Virginia Apgar in 1952 as a rapid neonatal assessment tool, originally developed to address inconsistency in delivery room practices. The Mosteller BSA formula was published in 1987, simplifying earlier more complex calculations for routine clinical use. The late 20th century saw the rise of clinical decision support systems embedding these formulas into hospital information technology, reducing calculation errors and improving bedside access to validated tools.
Frequently Asked Questions
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.
What is the average BSA for adults?
The average BSA for adults varies by population but is approximately 1.73 square meters, which is the value historically used as the reference standard for normalizing physiological measurements. In North American and European populations, average adult male BSA is approximately 1.9 square meters, while average adult female BSA is approximately 1.6 square meters. BSA varies considerably with body size, ranging from approximately 1.2 square meters for a petite adult to over 2.5 square meters for very large individuals. In pediatric populations, BSA ranges from about 0.2 square meters in neonates to adult values by late adolescence. The 1.73 square meter standard was established in the early twentieth century and is used to normalize glomerular filtration rate and other renal function measurements.
How does BSA relate to burn assessment?
BSA plays a critical role in burn injury assessment and management. The total body surface area affected by burns determines fluid resuscitation requirements, hospital admission criteria, and treatment protocols. The Rule of Nines divides the adult body surface into regions that are each approximately 9 percent or multiples of 9 percent of total BSA: head 9 percent, each arm 9 percent, each leg 18 percent, anterior trunk 18 percent, posterior trunk 18 percent, and perineum 1 percent. The Lund-Browder chart provides more accurate age-specific BSA percentages, particularly important in pediatric patients whose body proportions differ from adults. The Parkland formula for fluid resuscitation calculates required fluid volume as 4 mL multiplied by patient weight in kg multiplied by percent total BSA burned.
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy