Body Surface Area Calculator

Body Surface Area (BSA) Calculator

If you've ever wondered why two people who weigh exactly the same can still need different medication doses, body surface area is usually the answer. Unlike weight alone, BSA takes both height and weight into account, which turns out to be a much better predictor of things like blood volume and organ size and that's exactly why doctors lean on it instead of weight for certain calculations. Our free BSA calculator gives you that number in seconds, using the same formula clinicians actually use.

Whether you searched for a body surface area calculator, wanted to know what BSA is or you're trying to understand how to calculate BSA for a class or a personal reason, here's the full picture.

What This Calculator Does

Enter your height and weight and the calculator returns your body surface area in square meters (m²), the standard unit used in clinical settings worldwide.

A quick note before we go further: this is genuinely a medical-style metric, more so than BMI or calorie needs. BSA shows up most often in hospitals and pharmacies, not gyms. So think of this tool as a way to understand your own number and the science behind it, not as a replacement for a doctor's calculation in any real medical decision.

How to Calculate BSA

There are several accepted formulas for BSA, but the one used most often today is the Mosteller formula, mainly because it's simple, easy to double-check by hand and accurate to within about 5% of more complex methods:

So for someone 170 cm tall weighing 70 kg, that works out to roughly 1.82 m².

A few other formulas exist too and you might see them referenced elsewhere:

• Du Bois formula (the original, from 1916): 0.007184 × weight^0.425 × height^0.725
• Haycock formula: generally considered more accurate for infants and children
• Gehan-George and Boyd formulas: less common alternatives, occasionally cited in research

Most adult clinical settings today default to Mosteller specifically because professional oncology guidance has pointed to it as one of the more accurate options available, while still being simple enough to calculate quickly at the bedside.

What Is a Normal BSA Range?

There isn't one single "normal" number, since BSA depends entirely on your height and weight. That said, here's roughly where most adults land:

• Typical adult range: about 1.5 to 2.2 m²
• Average adult female: around 1.6 to 1.8 m²
• Average adult male: around 1.9 to 2.0 m²
• Newborns: as low as 0.2 to 0.25 m², rising quickly through childhood

Unlike BMI, there isn't a "healthy vs. unhealthy" category system for BSA. A higher or lower number simply reflects your body size; it isn't, by itself, a sign of anything being wrong.

How BSA Is Used in Medicine

This is really where BSA earns its keep and it's worth understanding even if you're not a healthcare professional.

• Chemotherapy dosing: Most chemotherapy drugs are dosed in milligrams per square meter (mg/m²) rather than a flat dose or a simple per-kilogram dose. This is because how a drug spreads through the bloodstream and organs correlates more closely with body surface area than with weight alone. Two patients who weigh the same but differ in height can end up needing meaningfully different chemo doses once BSA is factored in.
• Burn assessment: Doctors use BSA-based methods (like the "rule of nines") to estimate what percentage of a patient's body has been burned, which directly shapes fluid resuscitation and treatment decisions.
• Other clinical uses: BSA also gets used to index measurements like cardiac output (giving a "cardiac index") and kidney function (glomerular filtration rate), so results can be fairly compared across patients of very different sizes.

How to Use Your Result

Use your number to understand the concept, not to self-dose anything. This calculator is educational.

• If you're a patient facing chemotherapy, your care team will calculate your BSA using clinical-grade measurements as part of your actual treatment plan. This tool can help you understand what that number means, but it isn't a substitute for it.
• If you're a student or caregiver, this is a solid way to see the math behind a concept you're studying or trying to understand for a loved one.
• Re-check your number if your weight changes meaningfully, since BSA shifts along with height and weight.

Limitations and Important Disclaimer

This tool is for general and educational reference only. It is not intended for clinical dosing decisions of any kind.

• BSA formulas are estimates, not exact measurements and can be less accurate at extremes of height or weight (very tall, very short, very high or very low body weight).
• This calculator doesn't account for edema, fluid retention, amputation or unusual body composition, all of which can affect real clinical BSA calculations.
• Always defer to a prescriber, pharmacist or your care team for any actual medication dosing, treatment planning or clinical decision involving BSA. This page is not medical advice.

Frequently Asked Questions

This content is based on standard clinical BSA formulas (Mosteller, Du Bois) and published oncology and clinical reference guidance. It is intended for general and educational purposes only, not medical advice. Any real medication dosing or treatment decision should always come from a qualified healthcare provider.