This BSA calculator works out your body surface area in square meters from just your height and weight, using the same formulas doctors, nurses, and pharmacists actually use — Mosteller, Du Bois, and Haycock. Enter your numbers once and see all three side by side, since the formula used can genuinely change the number, and it helps to see how much.
What this number is actually used for:
Body surface area shows up in a few specific clinical contexts: dosing certain chemotherapy drugs, assessing what percentage of the body a burn covers, normalizing cardiac output measurements, and adjusting kidney function tests. It is genuinely useful information — and also genuinely not something to self-apply to any treatment decision. If a doctor, pharmacist, or nurse has asked for your BSA, this calculator can show you the number and the formula behind it, but the dose or clinical decision built on that number needs to come from them, not from this page. If you’re looking for a more general body-composition number instead, our BMI Calculator Philippines or Ideal Weight Calculator is probably closer to what you need.
What is BSA, and why does it need its own calculator?
Body surface area (BSA) is an estimate of the total external surface of your body, expressed in square meters. It sounds like an odd thing to measure, but it turns out to correlate with several important physiological processes — metabolic rate, blood volume, and cardiac output all scale more closely with body surface area than with weight alone. That is precisely why it was developed in the first place: in 1916, physicians Eugene and Delafield Du Bois needed a more reliable way to estimate metabolic rate than weight-based formulas were providing, and BSA became the standard.
Today, according to a clinical overview published by the NIH, BSA is used most heavily in oncology for calculating chemotherapy doses, since many chemotherapeutic agents have a narrow safety margin where dosing by weight alone would be too imprecise. It also comes up in burn assessment (what percentage of a patient’s BSA is affected), cardiology (indexing cardiac output and valve area to body size), and nephrology (adjusting kidney function measurements for body size).
How this calculator works
Since nobody can practically measure their own external body surface area with a tape measure, every BSA formula in use today is a mathematical estimate built from height and weight instead. Three formulas have earned the most trust and use over the past century, and this calculator runs all three:
Mosteller formula (1987) — the most commonly used today
BSA (m²) = square root of [ (height in cm × weight in kg) ÷ 3600 ]
Developed by Dr. Richard Mosteller specifically because it could be calculated on a basic pocket calculator, this formula has become the most widely used BSA equation in current clinical practice, largely for that simplicity.
Du Bois formula (1916) — the original reference formula
BSA (m²) = 0.007184 × weight(kg)^0.425 × height(cm)^0.725
The original BSA formula, and for decades considered the gold standard, though it was derived from direct measurements of only nine people. Research since has found it tends to overestimate BSA in people with obesity by a meaningful margin, which is part of why Mosteller has become more common in general use.
Haycock formula (1978) — commonly used for children
BSA (m²) = 0.024265 × height(cm)^0.3964 × weight(kg)^0.5378
Developed specifically to handle body proportions across a wide age range, including infants and children, whose height-to-weight ratios differ substantially from adults.
The formulas rarely disagree by a large margin for an average-sized adult — often within a few percent of each other — but the gap widens at the extremes, particularly for people with obesity or very young children, which is exactly why seeing all three matters more than trusting a single number blindly.
How to use this BSA calculator
Enter your height and weight
Height in centimeters, weight in kilograms. No unit conversion required beforehand — the calculator handles the formula math directly in metric, which is how all three formulas were originally derived.
Choose a formula
Mosteller is set as the default since it is the most commonly used in general clinical practice today. If a specific formula was requested by a doctor or referenced in a document you’re working from, select that one instead — Du Bois if you need the classic reference calculation, Haycock if the context involves a child.
Read your result
Your BSA appears in square meters, with the equivalent in square feet underneath for reference. Below that, all three formulas are shown side by side, so you can see exactly how much (or how little) the choice of formula changes your number.
Average BSA reference values
For general context, here is roughly where most adults fall — useful as a sanity check on your result, not as a target to aim for:
- Average adult male: approximately 1.9 m²
- Average adult female: approximately 1.6 m²
- Typical adult range: roughly 1.5 to 2.2 m², depending on height and weight
These are population averages, not clinical targets — BSA scales with body size, so a taller or larger-framed person will have a higher BSA without that meaning anything is wrong.
Frequently asked questions
How do you calculate BSA formula results by hand?
Using the Mosteller formula, multiply your height in centimeters by your weight in kilograms, divide that by 3600, then take the square root of the result. For example, someone who is 170 cm tall and weighs 70 kg would calculate (170 × 70) ÷ 3600 = 3.31, then the square root of 3.31, giving a BSA of about 1.82 m². The Du Bois and Haycock formulas use exponents instead of a square root and are far more practical to calculate with a tool than by hand.
Which BSA formula is the most accurate?
None of the three is universally “most accurate” — each was validated against different populations and has different known limitations. Mosteller is the most widely used today for its simplicity and reasonable accuracy across most adults. Du Bois is historically significant but tends to overestimate BSA in people with obesity. Haycock was built specifically for pediatric accuracy. When a specific formula is required for a medical or clinical purpose, use the one that was specified rather than picking based on which gives a particular number.
Why do the three formulas give slightly different results?
Each formula was derived from a different, relatively small study population, using different statistical relationships between height, weight, and measured body surface area. For an average-sized adult, the differences are usually small — often under 5 percent — but they grow larger for people with obesity, very short or tall stature, or very young children, since none of the original study populations fully represented those groups.
What is BSA used for in medicine?
The most common clinical use is calculating doses for certain chemotherapy drugs, where BSA-based dosing is considered more precise than dosing by weight alone. It is also used to estimate the percentage of the body affected by burns, to index cardiac measurements like cardiac output and valve area to body size, and to adjust kidney function tests for a person’s size.
Can I use this calculator to work out my own chemotherapy dose?
No — this calculator only provides the BSA number itself, in square meters. Actual chemotherapy dosing depends on the specific drug, protocol, your full medical history, and clinical judgment that only your oncology team can apply. Never use a BSA figure from this or any online calculator to determine or adjust a medication dose yourself.
What is a normal BSA range for adults?
Most adults fall somewhere between about 1.5 and 2.2 m², with the population average landing around 1.9 m² for men and 1.6 m² for women. BSA scales directly with body size, so there is no single “ideal” number to aim for — a taller or larger-framed person will naturally have a higher BSA without that indicating anything about their health.
Does BSA change with weight loss or gain?
Yes, since BSA is calculated directly from height and weight, any meaningful weight change will shift the result. Height stays fixed in adulthood, so weight is the variable driving most BSA changes over time for the same person.
Related calculators
A few other body-composition tools that use similar measurements:
BMI Calculator Philippines — See where your weight falls relative to your height on the standard BMI scale.
Ideal Weight Calculator — Get a healthy weight range based on your height and gender.
Waist to Hip Ratio Calculator — Check a different body-proportion health marker using waist and hip measurements.
Body Fat Calculator — Estimate your body fat percentage from a few simple measurements.