About the Body Surface Area Calculator
Body surface area estimates the total external area of the body in square metres. It is the standard basis for chemotherapy dosing, burn assessment, and calculating cardiac index, because many physiological processes scale with surface area rather than with weight.
The formula
Mosteller: BSA = √(height cm · weight kg / 3600)The Mosteller formula is the simplest and most widely used. The DuBois formula, BSA = 0.007184 · height^0.725 · weight^0.425, predates it and remains common in cardiology.
How to use this calculator
- 1Enter your Weight (kg). The field starts at
70, which you can overwrite. - 2Enter your Height (cm). The field starts at
170, which you can overwrite. - 3Read the result straight away — it recalculates as you type, so there is no button to press. Use Share to copy a link that reopens the page with your exact numbers filled in.
Worked example
| Input | Value |
|---|---|
| Weight (kg) | 70 |
| Height (cm) | 170 |
Result
DuBois Formula: 1.810 m²
Mosteller Formula: 1.818 m²
Haycock Formula: 1.826 m²
(Average adult: ~1.7–1.9 m²)
Those are the values the page loads with, so you can reproduce this result yourself and then change one field at a time to see what drives the outcome.
Understanding your result
Surface area is used instead of weight because metabolic rate, blood volume, and renal clearance all track it more closely. This matters most in oncology, where the therapeutic window for a cytotoxic drug is narrow — dosing by weight alone would under-treat some patients and poison others.
The various formulas agree closely for average adults but diverge at the extremes of size, particularly in obesity and in small children. Different formulas can differ by 5 percent or more in those ranges, which is why clinical protocols specify which one to use rather than leaving it to preference.
Things worth knowing
- A typical adult BSA is around 1.7 square metres, with 1.9 often used for men and 1.6 for women in rough estimates.
- Mosteller is preferred for its simplicity and can be computed at the bedside; DuBois remains standard in some cardiology contexts.
- Cardiac index is cardiac output divided by BSA, which is what makes it comparable between patients of different sizes.
- In burns assessment, the rule of nines estimates the percentage of BSA affected, which drives fluid resuscitation.
- Never use this for actual drug dosing. Clinical dosing requires verified measurements and pharmacy calculation.
Frequently asked questions
What is body surface area used for?+
Chemotherapy dosing, calculating cardiac index, assessing burn extent, and determining paediatric fluid requirements — all situations where physiology scales with surface area better than with body weight.
Which BSA formula is most accurate?+
Mosteller and DuBois agree closely for average adults. Mosteller is simpler and more common in modern practice; DuBois persists in cardiology. They diverge most at extremes of body size.
What is a normal BSA for an adult?+
Roughly 1.6 to 2.0 square metres, with 1.7 as a common average. Men typically sit a little higher than women, and it scales with both height and weight.
Why dose drugs by surface area rather than weight?+
Because metabolic rate and drug clearance correlate better with surface area. For drugs with a narrow safety margin such as cytotoxics, this reduces both under-treatment and toxicity.