What is body surface area (BSA) used for?

BSA is used to adjust or standardize certain medical calculations. A common use is medication dosing written per square meter (m²). It may also be used to index some clinical measurements to body size.

Is BSA the same thing as BMI?

No. BMI estimates weight category using height and weight. BSA estimates the body's surface area in m². They serve different purposes.

Which BSA formula is most commonly used?

Many tools default to the Mosteller method because it's simple and widely accepted. Some clinicians prefer other formulas depending on the situation.

Why do different BSA formulas give different results?

Each formula was developed from different datasets and assumptions. Differences are usually small, but they can matter in certain clinical settings.

Can I use this calculator to dose medication myself?

You can calculate BSA, but you should not self-dose. Medication dosing depends on many factors (condition, drug type, kidney/liver function, and prescribing rules). Use BSA only as part of a clinician-guided plan.

Does BSA change if I lose or gain weight?

Yes. Since weight is part of the calculation, BSA typically changes when weight changes. Height changes are usually minimal in adults.

What unit should my BSA result be in?

BSA is commonly reported in square meters (m²). That's the standard unit used in many medical calculations.

Is BSA accurate for athletes or very muscular people?

BSA is still an estimate based on height and weight. Body composition can affect how well any formula matches true surface area, so clinicians may interpret results with context.

Can this be used for children and infants?

BSA is often used in pediatrics, but the preferred formula can vary. If your clinician specifies a method, use that same formula for consistency.

What should I do if my height is in feet and inches?

Use the unit switch (if available) or convert your height to centimeters before calculating. Accurate unit entry is key for a correct result.

Body Surface Area Calculator (BSA) – Fast & Simple

This calculator estimates your body surface area (BSA) using your height and weight. BSA is the outside area of the body, shown in square meters (m²). It is commonly used in healthcare to help standardize certain measurements, and it may be used when a medicine dose is prescribed "per m²." This tool can help patients, caregivers, students, and clinicians quickly get a BSA estimate without manual steps. You enter height and weight, and the calculator returns your estimated BSA value in m², which you can use for comparisons or calculations that require BSA.

How to Use This Calculator

Enter your height (choose cm, feet/inches, or meters if options are available).
Enter your weight (choose kg or lb if options are available).
Select a formula if the calculator offers multiple methods (Mosteller is common).
Click Calculate.
Read your BSA result in m² and use it where needed (for example, dose-per-m² calculations).

What This Calculator Measures

Body surface area (BSA) is an estimate of the total surface area of the human body.

BSA (m²): The result is shown in square meters.
Height and weight: These are the inputs used to estimate surface area.
Estimate: BSA is not measured directly here—it's calculated from formulas that approximate surface area based on body size.

BSA is often used to normalize other values (so results are easier to compare across different body sizes) and to support dose calculations when a healthcare provider uses m²-based dosing.

Formula or Logic

Most calculators use one of several well-known BSA formulas. A common option is the Mosteller formula because it is simple and widely used.

Here's the idea in plain language:

Multiply your height and weight together.
Scale that number down (so units work out properly).
Take a square root to convert it into an area-like estimate.
The final answer is your BSA in m².

Some tools also offer other formulas (like Du Bois, Haycock, or Gehan & George). These may give slightly different results, especially for very small children or unusual body proportions.

Example Calculations

Example 1

Height: 170 cm
Weight: 60 kg
Estimated BSA: 1.68 m²

Example 2

Height: 180 cm
Weight: 80 kg
Estimated BSA: 2.00 m²

Example 3

Height: 155 cm
Weight: 50 kg
Estimated BSA: 1.47 m²

Understanding Your Results

Your BSA result is a single number in m² that represents your estimated body surface area.

What it can be used for:

Dose calculations when a prescription is written as "mg per m²."
Indexing medical values to body size (for example, some heart and kidney measures may be adjusted using BSA).
Comparisons over time, such as before/after weight change (using the same formula each time).

Important notes:

This is an estimate, not a direct measurement.
Small input changes (like a few kg) can change BSA.
For medication dosing, always follow a clinician's instructions.

BSA varies widely by age, height, weight, and body composition, so a single "normal" range is not reliable for everyone. Use your result in the specific context it's intended for (such as a dosing order or an indexed medical measurement).

Common Mistakes to Avoid

Mixing units (entering pounds while "kg" is selected).
Typing height in meters when the field expects centimeters.
Using guessed height/weight instead of current values.
Comparing results from different formulas without noting the method.
Rounding too early when doing dose-per-m² math.
Using BSA as a health "score" (it's not a diagnosis tool).
Calculating for children without using the formula your clinician prefers.

Body surface area (BSA) is a simple but useful estimate based on your height and weight. It's commonly used for m²-based dosing and for indexing certain clinical measurements to body size. Enter accurate values, keep units consistent, and use the same formula when comparing results over time. Try the calculator above to see your results.

Frequently Asked Questions

Common questions about the Body Surface Area Calculator are answered below.

Body Surface Area Calculator