The body surface area calculator above estimates the total surface area of your skin β usually written as BSA and measured in square meters (mΒ²) β using height and weight rather than a physical scan. It's not a beauty or fitness metric; BSA is a real clinical tool used to normalize drug dosing, especially chemotherapy, and to index measurements like cardiac output so they can be fairly compared between a small person and a large one. This calculator runs your numbers through the three formulas doctors and pharmacists reference most: Du Bois, Mosteller, and Haycock.
Arb Digital builds practical, evidence-based calculators like this one for health, wellness, and medical-adjacent websites that want to earn trust with genuinely useful content, not filler. Enter your height and weight above, choose which formula you want highlighted as your headline number, and you'll instantly see all three results side by side along with their average.
What This Body Surface Area Calculator Does
The tool takes your height and weight and runs them through three separate, independently derived mathematical formulas, each of which estimates total skin surface area in square meters. Because the three formulas were built from different research datasets and slightly different mathematical approaches, they don't always agree exactly β most healthy adults will see results within a few hundredths of a square meter of each other across all three. The calculator shows you Du Bois, Mosteller, and Haycock results individually, plus their average, so you can see both the individual clinical formulas and a consensus estimate in one place. You can switch between metric (kilograms and centimeters) and imperial (pounds and inches) units at any time.
How to Use It
- Choose your unit system β metric (kg/cm) or imperial (lb/in) β using the toggle buttons.
- Enter your height in the height field.
- Enter your weight in the weight field.
- Pick a preferred formula from the dropdown β Mosteller is the simplest and most widely used in modern clinical practice, but Du Bois and Haycock are also common depending on the protocol.
- Press Calculate My BSA. The big number reflects your chosen formula; the grid below shows all three formulas plus the average so you can compare.
The Formulas β How BSA Is Calculated
All three formulas take height (in centimeters) and weight (in kilograms) as inputs and return BSA in square meters:
- Du Bois & Du Bois (1916): BSA = 0.007184 Γ Weight0.425 Γ Height0.725. The oldest and historically most referenced formula, originally derived from just nine subjects, but still widely cited as a clinical baseline.
- Mosteller (1987): BSA = β(Height Γ Weight Γ· 3600). By far the simplest formula to compute and verify by hand, which is a big part of why it has become the most commonly used formula in modern hospital pharmacy and oncology software.
- Haycock (1978): BSA = 0.024265 Γ Weight0.5378 Γ Height0.3964. Developed using a broader dataset that specifically included infants and children, so it's often preferred in pediatric contexts.
You can read background on BSA-based dosing and its clinical rationale from the National Cancer Institute's dictionary of cancer terms at Cancer.gov (NCI), and general physiological reference ranges are discussed by the National Institutes of Health at NIH.gov (NCBI).
Why BSA Matters More Than Weight Alone in Medicine
Weight-based drug dosing seems intuitive β a bigger person gets more medication β but weight alone is a surprisingly imprecise proxy for how a drug will actually distribute and act inside the body. Two people can weigh exactly the same while having very different amounts of muscle, fat, and organ mass, and drugs interact with living, metabolically active tissue rather than with fat storage. Body surface area correlates more closely than weight does with several physiological variables that matter for dosing: blood volume, cardiac output, kidney filtration rate, and basal metabolic rate all scale more predictably with BSA than with raw body weight. That's precisely why chemotherapy drugs, several cardiac medications, and burn-treatment fluid calculations are dosed in milligrams per square meter (mg/mΒ²) rather than milligrams per kilogram in many protocols. It's also why BSA is used to index cardiac output into "cardiac index," letting doctors fairly compare heart performance between a petite adult and a much larger one without size alone skewing the numbers.
Du Bois vs. Mosteller vs. Haycock: Which Should You Trust?
In practice, the three formulas rarely diverge by more than a few percent for an average-sized adult, and clinicians don't generally treat one as "more correct" in isolation β they use whichever formula their specific institution's protocol or drug-dosing software specifies, because dosing tables and clinical trial data were built around a particular formula. Du Bois remains historically significant and is still embedded in many older calculators and textbooks. Mosteller has become the de facto default in many U.S. hospital systems because it's easy to verify and reproduce without a calculator that supports fractional exponents β it's literally just a square root of a simple multiplication and division. Haycock is favored in pediatric and neonatal settings because its underlying data specifically included infants and small children, populations where Du Bois' original nine-adult dataset is a poor match. For a healthy adult using this tool for general curiosity or fitness tracking rather than a specific drug protocol, the average of all three, shown in the results grid, is a reasonable single estimate to reference.
Practical, Everyday Uses of Your BSA Number
Outside a hospital, BSA still shows up in a few places worth knowing about. Some burn-treatment guidance uses percentage of total body surface area affected to estimate severity and fluid resuscitation needs. Some fitness and physiology calculators use BSA alongside weight to estimate sweat rate and heat-dissipation capacity during exercise, since a larger surface area relative to mass allows faster heat loss. Researchers sometimes use BSA to normalize other physiological measurements β such as certain lab values or cardiac measurements β across people of different sizes so results can be compared fairly, similar to how BSA-based chemotherapy dosing tries to account for size differences between patients. None of these everyday applications require clinical precision, which is exactly the use case this free calculator is built for β a solid estimate, not a medical-grade dosing tool.
If body composition and size metrics interest you, our BMI Calculator and Lean Body Mass Calculator offer complementary ways to look at the same underlying data from different angles.
Arb Digital builds clear, fast, trustworthy websites and free calculators like this one for health and medical-adjacent brands. Browse more free tools below.
Try the Water Weight Calculator All Free ToolsCommon Mistakes to Avoid
- Using this for actual medical dosing. This tool is an educational estimate; real drug dosing must use the exact formula and rounding rules specified by a treating clinician or pharmacy protocol.
- Mixing unit systems. Entering height in inches while weight is still set to kilograms (or vice versa) will produce a meaningless result β always confirm both fields match your selected unit toggle.
- Assuming all three formulas must match exactly. Small differences between Du Bois, Mosteller, and Haycock are normal and expected; they were derived from different datasets.
- Ignoring which formula a specific protocol requires. If you're comparing your number to a clinical reference range, check which formula that reference used.
- Confusing BSA with body fat or BMI. BSA measures skin surface area, not fatness or weight status β a very muscular person and a very lean person of the same height and weight will have nearly identical BSA despite very different body composition.
Related Free Tools From Arb Digital
Explore more of your body's numbers with the BMI Calculator, Body Fat Calculator, Lean Body Mass Calculator, Waist-to-Height Ratio Calculator, or the Water Weight Calculator. See everything we offer in our free online tools hub.
Frequently Asked Questions
BSA is used clinically to dose certain medications, especially chemotherapy, and to normalize measurements like cardiac output so they can be fairly compared between people of different sizes. It correlates more closely with metabolic mass than weight alone.
No single formula is universally "most accurate" β Du Bois, Mosteller, and Haycock were derived from different datasets and are each used in different clinical contexts. Mosteller is the most commonly used today because of its simplicity; Haycock is often preferred in pediatrics.
Average adult BSA is roughly 1.6 to 1.9 mΒ² for women and 1.9 to 2.2 mΒ² for men, though this varies with height and weight. There is no single "ideal" BSA β it simply reflects your body size.
BMI estimates weight status relative to height using a single formula. BSA estimates total skin surface area and is used differently in medicine, primarily for drug dosing and physiological normalization rather than weight classification.
No. This tool is for general education and estimation only. Actual medical dosing must be calculated and verified by a licensed clinician or pharmacist using the exact formula and rounding specified in the treatment protocol.
Each formula was derived from a different research dataset using different statistical methods and study populations, so small variations between them are expected and normal, especially at the extremes of height and weight.
This tool provides general estimates for educational purposes only and is not medical advice. Individual needs vary β consult a doctor before making health decisions.
