Body Surface Area Calculator
Calculate body surface area in m² with Mosteller, DuBois and Haycock formulas — used in medicine and dosage calculations.
Body surface area
1.818 m²
Mosteller formula (most common)
DuBois formula
1.81 m²
Haycock formula
1.826 m²
BSA is used in clinical settings to dose some medicines and interpret cardiac measurements. The three formulas agree closely for typical adult builds.
Last updated: March 2026
How this calculator is verified
Checked by True Calculator automated test suite on
- Formula verified against a published worked example in the automated test suite
- Edge cases (zero, negative, boundary and unit-mismatch inputs) covered by unit tests
The full verification method is on our how we verify page. Found an error? Tell us and we will re-check it.
When to Use This Calculator
Use the body surface area calculator when you need a quick BSA figure — students preparing for physiology exams, nurses or pharmacy students double-checking dose calculations, or anyone reading a report that mentions body surface area and wanting to understand the number. BSA is used to express cardiac index, to normalise kidney filtration rates (eGFR), and in some chemotherapy dosing, so the tool is genuinely useful in clinical study contexts. It also appears in health research and fitness devices that normalise values by body size. Since the three formulas agree closely, the tool builds confidence: whatever method a textbook or clinician prefers, the result is essentially the same. It takes seconds and needs only weight and height.
How to Use This Calculator
- Step 1: Enter your weight in kilograms.
- Step 2: Enter your height in centimetres, which is needed for the BSA formula.
- Step 3: Read the body surface area from the Mosteller formula.
- Step 4: Compare with the DuBois and Haycock estimates, which should be very close.
Worked Example
For a 70 kg adult of 170 cm, the Mosteller formula — the square root of height times weight divided by 3600 — returns 1.818 m². The older DuBois equation gives 1.81 m² and Haycock gives 1.826 m², all agreeing within a couple of percent. A larger person of 85 kg and 180 cm gets about 2.06 m². These numbers matter in medicine because some drug doses are calculated per square metre of body surface, and the close agreement between formulas means the choice of formula rarely changes a practical dose.
Tips and Common Mistakes
- •Tip 1: Use the Mosteller value by default, since it is the most widely used in modern practice.
- •Tip 2: Recalculate after significant weight changes — a 10 kg shift changes BSA by only a few percent.
- •Tip 3: If a doctor mentions your BSA, confirm which formula they used so the numbers line up.
- ✗Mistake 1: Mixing units — height in centimetres with weight in pounds will produce a meaningless number.
- ✗Mistake 2: Assuming BSA equals fitness or health; it is a size metric for medical calculations, not an assessment.
Frequently Asked Questions
What is body surface area (BSA)?
It is the total surface area of the human body in square metres, estimated from height and weight. A typical adult has about 1.7–2 m² depending on size.
Which formula should I use?
The Mosteller formula is the most widely used and easiest to remember: √(height cm × weight kg ÷ 3600). DuBois and Haycock are older or specialised alternatives that agree closely for normal builds.
Why is BSA used in medicine?
Some medications, especially chemotherapy drugs, are dosed per square metre of body surface rather than per kilogram, and cardiac measurements like cardiac index are expressed per m².
Can I calculate it at home?
Yes — with your weight and height you can estimate it in seconds with this calculator. It is only an estimate though; hospital dosing always uses the clinician's own measurement and formula choice.
Does BSA change with weight loss?
Yes, it falls slowly because the height term stays fixed. Losing 10 kg typically reduces BSA by only a few percent, which is why the formulas are most useful for comparing across people, not day to day.
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