🧬Body Surface Area Calculator
Calculate body surface area (BSA) using three validated formulas including Mosteller, DuBois, and Haycock. Used in medical dosing, burn assessment, and cardiac index calculations.
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Average BSA (m²)
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Body surface area (average of 3 formulas): 1.818 m² (within typical range for males, typical range: 1.7–2.1 m²). Mosteller: 1.818 m², DuBois: 1.810 m², Haycock: 1.826 m². Note: BSA is used in medical dosing for chemotherapy and certain medications.
BSA by Formula (m²)
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Body Surface Area Calculator: Medical Uses, Formulas, and Normal Values
A body surface area calculator estimates the total external surface area of the human body, expressed in square meters (m2). While most people are unfamiliar with BSA as a personal health metric, it is a foundational number in clinical medicine. This BSA calculator uses three validated formulas to give you an accurate estimate based on your height and weight, along with context for what that number means in medical practice.
How to Calculate Body Surface Area for Medication Dosing
BSA is used in medicine because it often predicts drug clearance and physiological capacity better than body weight alone. A person who is twice as heavy does not necessarily have kidneys or a liver that are twice as efficient at processing drugs. Body surface area scales more closely with organ function, blood volume, and metabolic capacity across a wide range of body sizes, making it a more reliable basis for dosing drugs with narrow therapeutic windows.
The most common application is chemotherapy. Cytotoxic drugs are toxic to rapidly dividing cells and have a narrow margin between an effective dose and a dangerous one. Dosing expressed as milligrams per square meter (mg/m2) allows oncologists to calculate the actual dose for each patient by multiplying the per-m2 dose by the patient's BSA. A patient with a BSA of 1.7 m2 receiving a drug dosed at 75 mg/m2 would receive 127.5 mg. This personalization reduces the risk of both underdosing (ineffective treatment) and overdosing (severe toxicity).
DuBois Body Surface Area Formula: The Historical Standard
The DuBois and DuBois formula, published in 1916, is the oldest and historically most cited BSA formula. Despite being derived from measurements on only nine subjects, it remained the clinical reference for decades. The formula is: BSA = 0.007184 x height (cm) raised to the power 0.725 x weight (kg) raised to the power 0.425. Because of its long history, many clinical reference values and dose adjustment tables were calibrated to DuBois BSA values, which is one reason it is still used today even when newer formulas may be more accurate.
The DuBois formula tends to underestimate BSA in individuals with obesity and may be less accurate at the extremes of body size. For most average-build adults, however, it produces results within 2 to 3 percent of values from newer formulas.
BSA Calculator for Chemotherapy Dosing: Mosteller and Haycock Formulas
Two formulas developed after the DuBois formula are now widely used in clinical practice, particularly for a BSA calculator for chemotherapy dosing.
Mosteller Formula (1987)
Published in the New England Journal of Medicine in 1987, the Mosteller formula is now the most widely adopted in clinical oncology because of its accuracy and simplicity. The formula is: BSA = the square root of (height in cm multiplied by weight in kg, divided by 3600). It requires only a square root calculation, making it easy to compute at the bedside without a calculator. Accuracy is comparable to more complex formulas for most adult patients, and it has been adopted as the standard by many cancer treatment centers and drug formularies.
Haycock Formula (1978)
Published by Haycock and colleagues in 1978 and validated specifically for pediatric patients, the Haycock formula is considered the most accurate for children and for adults who fall significantly outside the average weight range. The formula is: BSA = 0.024265 x height (cm) raised to the power 0.3964 x weight (kg) raised to the power 0.5378. It is the preferred formula in pediatric oncology when calculating chemotherapy doses for children, where body size varies enormously and accurate BSA estimation is especially critical.
Normal Body Surface Area Values by Age Group
Understanding where your BSA falls relative to typical values helps contextualize your result:
- Newborn infant: approximately 0.25 m2
- 2-year-old child: approximately 0.5 m2
- 10-year-old child: approximately 1.1 m2
- Average adult woman: approximately 1.6 m2
- Average adult man: approximately 1.9 m2
- The clinical "standard patient" reference used in pharmacology: 1.73 m2
- Very tall or heavy adults: 2.2 m2 and above
Other Medical Uses of Body Surface Area
Beyond drug dosage calculation, BSA appears in several other clinical contexts. In cardiology, cardiac index is cardiac output (liters of blood per minute) divided by BSA, producing a size-normalized measure of heart performance. A normal cardiac index is 2.5 to 4.0 liters per minute per m2, and this metric is used during cardiac catheterization and intensive care monitoring. In burn medicine, the Rule of Nines divides the body surface into anatomical regions each representing roughly 9 percent of total BSA. Emergency physicians use this to estimate the percentage of total BSA affected by a burn, which then drives fluid resuscitation calculations. Skin surface area calculations in dermatology use similar principles when estimating the extent of skin conditions like psoriasis or eczema for treatment planning.
How Does BSA Differ from BMI?
BMI (body mass index) is a ratio of weight to height squared and is used primarily as a population-level screening tool for underweight, overweight, and obesity. It does not directly estimate any physical area or volume of the body. BSA, by contrast, estimates actual surface area and is used specifically in clinical dosing contexts where the size of the body matters for drug distribution. BMI cannot be substituted for BSA in drug dosing calculations. A tall, muscular person and a shorter, heavier person might have the same BMI but very different BSA values, which would result in meaningfully different drug doses.
Frequently Asked Questions
What is body surface area used for in medicine?
Body surface area is used primarily for calculating doses of drugs with narrow therapeutic windows, most notably chemotherapy agents. It is expressed as a dose per square meter (mg/m2) to account for differences in body size and organ function across patients. BSA is also used in cardiology to calculate cardiac index (cardiac output normalized to body size), in burn medicine to estimate the extent of skin injury for fluid resuscitation, and in dermatology to quantify the extent of skin conditions such as psoriasis.
Which BSA formula is most accurate?
For average-build adults, all three major formulas (Mosteller, DuBois, Haycock) produce results within 2 to 3 percent of each other. The Mosteller formula is the most widely used in oncology practice today because it is accurate and simple to compute. The Haycock formula is generally considered most accurate for children and for adults significantly above or below average weight. The DuBois formula is historically important and still used where reference tables were calibrated to its values. Averaging all three, as this calculator does, minimizes the error of any single formula.
How do I calculate body surface area?
The simplest method is the Mosteller formula: take your height in centimeters, multiply it by your weight in kilograms, divide by 3600, and then take the square root. For a person who is 170 cm tall and weighs 70 kg: (170 x 70) divided by 3600 = 3.306, and the square root of 3.306 is approximately 1.82 m2. This calculator performs this calculation automatically and also runs the DuBois and Haycock formulas for comparison.
How does BSA differ from BMI?
BSA and BMI are entirely different measurements used for different purposes. BMI is a ratio of weight to height squared (kg/m2) used as a screening index for population-level weight classification. BSA estimates the actual surface area of the skin in square meters and is used in clinical settings for drug dosage calculation, cardiac index, and burn assessment. BMI cannot be substituted for BSA in any medical dosing context. Two people with the same BMI can have meaningfully different BSA values depending on their height and body composition, which would result in different appropriate drug doses.