Body Surface Area Converter
Our free human metrics converter handles body surface area conversions. See tables, ratios, and examples for quick reference.
Body Surface Area Converter
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Formula: BSA (DuBois) = 0.007184 x Weight^0.425 x Height^0.725
Worked example โ BSA: 1.8136 m2 | Sample dose (75 mg/m2): 136.0 mg | Cardiac Index: 2.76
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 70^0.425 = 6.396 170^0.725 = 49.95 BSA = 0.007184 x 6.396 x 49.95 = 1.8136 m2 Mosteller check: sqrt((70 x 170) / 3600) = sqrt(3.306) = 1.8182 m2 Drug dose at 75 mg/m2: 1.8136 x 75 = 136.0 mg Cardiac 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 = 0.007184 x 4.217 x 39.09 = 1.1841 m2 Haycock: BSA = 0.024265 x 25^0.5378 x 120^0.3964 = 0.024265 x 5.476 x 8.858 = 0.9271 m2 The Haycock formula is preferred for children and gives a lower estimate. Drug 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.
Which BSA formula should I use?
The DuBois formula, published in 1916, remains the most widely used and cited BSA formula in clinical practice and medical literature. However, the Mosteller formula is increasingly popular because of its simplicity: BSA = square root of (weight x height / 3600). Both formulas give similar results for average-sized adults. The Haycock formula is preferred for pediatric patients because it was developed using data that included children and infants. The Boyd formula is sometimes used for very obese or very thin patients. In practice, the differences between formulas are typically small (within 5%) for normal-weight adults, but can diverge more significantly at extreme body sizes. Most oncology practices specify which formula to use in their treatment protocols.
How is BSA used in chemotherapy dosing?
Chemotherapy drugs are among the most toxic medications used in clinical practice, with narrow therapeutic windows between effective treatment and dangerous side effects. BSA-based dosing adjusts the drug amount to the patient's body size, theoretically accounting for differences in drug distribution, metabolism, and clearance. A typical chemotherapy dose might be prescribed as 75 mg/m2 of BSA, meaning a patient with BSA of 1.8 m2 would receive 135 mg. While BSA-based dosing has been standard practice for over 50 years, recent research suggests it does not perfectly predict drug pharmacokinetics, and some newer targeted therapies use flat (fixed) dosing instead. Nevertheless, BSA remains the standard for most cytotoxic chemotherapy agents.
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.
How is the cardiac index derived from BSA?
Cardiac index is cardiac output divided by body surface area, expressed in liters per minute per square meter. Indexing removes body size from the comparison, so the circulation of a small adult, a large adult and a child can be evaluated on the same scale. A cardiac output of 5.0 liters per minute in a patient with a BSA of 1.8 m2 gives a cardiac index of 2.78 L/min/m2. Stroke volume is indexed the same way to give stroke volume index.
Why does body surface area scale with roughly the two-thirds power of mass?
For geometrically similar shapes, area grows with the square of a linear dimension while volume, and therefore mass, grows with the cube. Eliminating the linear dimension leaves area proportional to mass raised to the two-thirds power. That is why every BSA formula uses fractional exponents rather than weight alone: the DuBois equation, for example, is 0.007184 multiplied by weight in kilograms to the 0.425 power and height in centimeters to the 0.725 power. Human bodies are not perfectly similar shapes, which is why the fitted exponents differ from the geometric ideal.
How do I convert a BSA in square meters to square feet?
Multiply by 10.7639, because one meter is 3.28084 feet and area scales with the square of that factor. A BSA of 1.8 m2 is therefore about 19.38 ft2, and 2.0 m2 is 21.53 ft2. Going the other way, divide square feet by 10.7639. Clinical practice almost universally reports BSA in square meters, so the square-foot figure is mainly useful for intuition about how much skin area the number represents.
Why is estimated GFR reported per 1.73 square meters?
Kidney clearance scales with body size, so kidney function results are normalized to 1.73 m2, a value taken as a representative average adult surface area, allowing values to be compared across patients of different sizes. That normalization is what you want for staging and trend-watching. When you need the patient's actual clearance rather than a size-normalized one, for example to size a renally cleared drug, convert back by multiplying the reported value by the patient's own BSA divided by 1.73.
Which patients show the largest disagreement between BSA formulas?
Disagreement widens at the edges of the range: infants and small children, very tall or very short adults, and people with substantial obesity. Each equation was fitted to a different reference sample, so extrapolating outside that sample is where they diverge, and the difference can exceed the few percent typical for average-sized adults. Because the choice of equation then changes a size-dependent calculation, institutions usually mandate one formula in their protocol so that results stay comparable between clinicians and over time.
How does BSA relate to burn assessment?
Burn severity is scored as a percentage of total body surface area involved, estimated with the rule of nines or, more precisely in children, a Lund and Browder chart that adjusts for the proportionally larger head of a young child. That percentage combined with body weight drives resuscitation planning. A BSA figure in square meters converts the percentage into a real area, which is what matters for dressing quantities and for estimating evaporative fluid and heat loss across the wound.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator ยท Editorial policy
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