Body Surface Area Converter
Our free human metrics converter handles body surface area conversions. See tables, ratios, and examples for quick reference.
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Formula
The DuBois formula estimates body surface area using weight in kilograms and height in centimeters raised to fractional powers. The Mosteller formula is simpler: BSA = sqrt(Weight x Height / 3600). The Haycock formula (BSA = 0.024265 x W^0.5378 x H^0.3964) is preferred for pediatric patients. Drug dosing multiplies BSA by the prescribed dose per square meter. Cardiac index = cardiac output / BSA.
Last reviewed: December 2025
Worked Examples
Example 1: Adult BSA Calculation
Example 2: Pediatric BSA Calculation
Background & Theory
The Body Surface Area Converter applies the following established principles and formulas. Unit conversion is the process of expressing a quantity in a different unit of measurement while preserving its physical meaning. At the foundation of modern measurement lies the International System of Units (SI), which defines seven base units: the meter for length, kilogram for mass, second for time, ampere for electric current, kelvin for thermodynamic temperature, mole for amount of substance, and candela for luminous intensity. All other units, called derived units, are defined as algebraic combinations of these seven. Dimensional analysis is the principal method for performing unit conversions. By treating units as algebraic quantities that can be multiplied, divided, and cancelled, a conversion factor chain allows a value expressed in one unit to be rewritten in another without altering its physical magnitude. For example, to convert 60 miles per hour to meters per second, one multiplies by a chain of conversion factors each equal to one: (1609.34 m / 1 mile) × (1 hour / 3600 s). Metric prefixes enable compact expression of quantities across extreme ranges of magnitude. Standard prefixes span from nano (10^-9) through micro (10^-6) and milli (10^-3) up through kilo (10^3), mega (10^6), and giga (10^9), and beyond in both directions. These prefixes are strictly multiplicative and apply consistently to any SI base or derived unit. Temperature conversions require affine transformations rather than simple scaling. To convert Celsius to Fahrenheit the formula is °F = (°C × 9/5) + 32, while the conversion to the absolute Kelvin scale is K = °C + 273.15. These formulas reflect the different zero points and degree-size conventions of each scale. Significant figures govern how precision is preserved through calculations. A result should not express more precision than the least precise input value permits. In digital storage, IEEE and IEC standards distinguish between decimal prefixes (kilobyte = 1000 bytes) and binary prefixes (kibibyte = 1024 bytes), a distinction that has practical consequences for how storage capacity is reported by manufacturers versus operating systems. Unit coherence — ensuring that all quantities in an equation share a consistent unit system — is essential for obtaining correct results.
History
The history behind the Body Surface Area Converter traces back through the following developments. Human beings have been measuring and comparing quantities since before recorded history. The earliest known measurement units were body-based: the cubit (the distance from elbow to fingertip), the foot, the hand, and the digit. The furlong originated as the length of a furrow a team of oxen could plow without resting. These anthropomorphic standards were practical for local use but differed between regions and kingdoms, creating persistent difficulties in trade and construction. The ancient Egyptians standardized the royal cubit at approximately 52.4 centimeters and distributed calibrated granite rods to ensure consistency across building projects, including the pyramids. Roman engineers used the mile (mille passuum, one thousand double paces) and spread these standards throughout their empire via road networks. Despite these efforts, measurement diversity persisted across medieval Europe, hampering commerce. The French Revolution created political will for radical standardization. In 1795 France officially adopted the metric system, defining the meter as one ten-millionth of the distance from the equator to the North Pole along the Paris meridian. This gave the world its first fully decimal, rationally constructed measurement system. The Metre Convention of 1875 established the International Bureau of Weights and Measures (BIPM) in Sevres, France, creating a permanent international body to maintain physical artifact standards and coordinate global metrology. For over a century, the kilogram was defined by a platinum-iridium cylinder locked in a vault near Paris. In 1999, a stark demonstration of what unit inconsistency costs occurred when NASA's Mars Climate Orbiter was lost because one engineering team used pound-force seconds while another used newton seconds. The spacecraft entered the Martian atmosphere at the wrong angle and was destroyed, at a cost of 327 million dollars. In 2019 the SI underwent its most significant revision, redefining all seven base units in terms of fixed numerical values of fundamental physical constants such as the speed of light, Planck's constant, and the elementary charge. This eliminated any reliance on physical artifacts and made the measurement system permanently stable and universally reproducible.
Frequently Asked Questions
Formula
BSA (DuBois) = 0.007184 x Weight^0.425 x Height^0.725
The DuBois formula estimates body surface area using weight in kilograms and height in centimeters raised to fractional powers. The Mosteller formula is simpler: BSA = sqrt(Weight x Height / 3600). The Haycock formula (BSA = 0.024265 x W^0.5378 x H^0.3964) is preferred for pediatric patients. Drug dosing multiplies BSA by the prescribed dose per square meter. Cardiac index = cardiac output / BSA.
Worked Examples
Example 1: Adult BSA Calculation
Problem: Calculate BSA for a patient weighing 70 kg and 170 cm tall using the DuBois formula.
Solution: DuBois: BSA = 0.007184 x 70^0.425 x 170^0.725\n70^0.425 = 6.396\n170^0.725 = 49.95\nBSA = 0.007184 x 6.396 x 49.95 = 1.8136 m2\nMosteller check: sqrt((70 x 170) / 3600) = sqrt(3.306) = 1.8182 m2\nDrug dose at 75 mg/m2: 1.8136 x 75 = 136.0 mg\nCardiac index: 5.0 / 1.8136 = 2.76 L/min/m2
Result: BSA: 1.8136 m2 | Sample dose (75 mg/m2): 136.0 mg | Cardiac Index: 2.76
Example 2: Pediatric BSA Calculation
Problem: Calculate BSA for a child weighing 25 kg and 120 cm tall.
Solution: DuBois: BSA = 0.007184 x 25^0.425 x 120^0.725\n= 0.007184 x 4.217 x 39.09 = 1.1841 m2\nHaycock: BSA = 0.024265 x 25^0.5378 x 120^0.3964\n= 0.024265 x 5.476 x 8.858 = 0.9271 m2\nThe Haycock formula is preferred for children and gives a lower estimate.\nDrug dose at 100 mg/m2 (Haycock): 0.9271 x 100 = 92.7 mg
Result: BSA (Haycock): 0.9271 m2 | BSA (DuBois): 1.1841 m2 | Dose (100 mg/m2): 92.7 mg
Frequently Asked Questions
What is Body Surface Area and why is it medically important?
Body Surface Area (BSA) is the total area of the external surface of the human body, measured in square meters. BSA is a critical measurement in clinical medicine because many physiological processes scale more closely with surface area than with body weight alone. It is most commonly used in oncology to calculate chemotherapy drug dosages, where even small dose variations can mean the difference between therapeutic efficacy and dangerous toxicity. BSA is also used to calculate the cardiac index (cardiac output divided by BSA), determine fluid resuscitation volumes for burn patients (using the rule of nines), adjust renal function markers like glomerular filtration rate, and set pediatric drug doses. The average adult BSA is approximately 1.7 m2 for women and 1.9 m2 for men.
How does BSA differ from BMI in assessing body size?
BSA and BMI both use height and weight but measure fundamentally different things. BMI (weight/height-squared) is a ratio that categorizes weight status (underweight, normal, overweight, obese) and is primarily used for epidemiological screening and general health assessment. BSA estimates the actual external surface area of the body in square meters and is used for clinical calculations like drug dosing and physiological indices. Two people with the same BMI can have different BSAs if their height and weight combinations differ. For example, a short heavy person and a tall lean person might share a BMI of 25 but have very different surface areas. BSA increases with both height and weight but is not a simple ratio; it follows a power-law relationship described by the various BSA formulas.
Can I use Body Surface Area Converter on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.
Does Body Surface Area Converter work offline?
Once the page is loaded, the calculation logic runs entirely in your browser. If you have already opened the page, most calculators will continue to work even if your internet connection is lost, since no server requests are needed for computation.
How do I interpret the result?
Results are displayed with a label and unit to help you understand the output. Many calculators include a short explanation or classification below the result (for example, a BMI category or risk level). Refer to the worked examples section on this page for real-world context.
Can I use the results for professional or academic purposes?
You may use the results for reference and educational purposes. For professional reports, academic papers, or critical decisions, we recommend verifying outputs against peer-reviewed sources or consulting a qualified expert in the relevant field.
References
Reviewed by Manoj Kumar, Mathematics Educator · Editorial policy