How much skin does an average adult have? The answer is roughly 1.7 to 1.9 square meters for many adults. Body surface area, or BSA, is that figure for one person, and clinicians use it to scale some treatments. The Body Surface Area Calculator estimates BSA from your height and weight.
It suits students, caregivers, and patients who want to see how the main formulas compare. The tool shows four BSA results at once, plus your BMI.
Table of Contents
- What the Calculator Does
- How to Use It, Step by Step
- The BSA Formulas
- Worked Example
- How to Read the Results
- Why Four Formulas Give Different Numbers
- BSA and Medication Doses
- Limitations and Assumptions
- FAQs About the Body Surface Area Calculator
What the Calculator Does
You enter height in centimeters and weight in kilograms. Results update as you type. There is no calculate button.
- Body Surface Area (Mosteller Formula): the large headline result, in square meters.
- DuBois Formula: a second estimate, in square meters.
- Haycock Formula: a third estimate, in square meters.
- Gehan & George Formula: a fourth estimate, in square meters.
- Body Mass Index (BMI): weight divided by height squared, in kg/m².
- A Copy BSA Results button and a Reset button.
How to Use It, Step by Step
- Enter Height (cm). The sample value is 175, and the tool accepts 30 to 250.
- Enter Weight (kg). The sample value is 70, and the tool accepts 2 to 500.
- Read the five result cards. All are shown to two decimals.
- Press Copy BSA Results to copy all four BSA values and BMI as one line of text.
- Press Reset to return to 175 cm and 70 kg.
If a value is blank or out of range, a red message names the field and every card shows N/A. Pressing Enter also recalculates. The tool uses metric units only. Multiply inches by 2.54 to get centimeters. Divide pounds by 2.2046 to get kilograms.
The BSA Formulas
Each formula uses height H in centimeters and weight W in kilograms. Mosteller is the simplest. The others use fitted powers of height and weight.
Height × Weight÷3,600→ √ =Mosteller BSA
- Mosteller: BSA = square root of (H × W ÷ 3,600).
- DuBois: BSA = 0.007184 × W^0.425 × H^0.725.
- Haycock: BSA = 0.024265 × W^0.5378 × H^0.3964.
- Gehan and George: BSA = 0.0235 × W^0.51456 × H^0.42246.
- BMI = W ÷ (H ÷ 100)².
Worked Example
Marcus is 175 cm tall and weighs 70 kg. Mosteller gives the square root of (175 × 70 ÷ 3,600). That is the square root of 3.4028, or 1.8447. BMI is 70 ÷ 1.75², or 22.857.
| Person | Mosteller | DuBois | Haycock | Gehan & George | BMI |
|---|
| Marcus, 175 cm, 70 kg | 1.84 | 1.85 | 1.85 | 1.85 | 22.86 |
| Grace, 160 cm, 55 kg | 1.56 | 1.56 | 1.57 | 1.58 | 21.48 |
| Child, 100 cm, 16 kg | 0.67 | 0.66 | 0.67 | 0.68 | 16.00 |
| Omar, 185 cm, 95 kg | 2.21 | 2.19 | 2.22 | 2.22 | 27.76 |
The units are square meters, except BMI in kg/m². The formulas agree within about 0.03 m² in these rows.
How to Read the Results
The big number is the Mosteller result, and the other three sit below it. A BSA of 1.84 m² means about 1.84 square meters of skin. Adults often fall roughly between 1.5 and 2.2 m², though healthy values vary widely.
BMI is added for context. It uses the same two inputs and says nothing about fat or muscle. The tool does not label BMI as under, normal, or over, and its note says BMI is not meaningful for children. For adult categories, use the BMI Calculator.
Why Four Formulas Give Different Numbers
Each formula came from a different set of measured people. Their fitted powers differ, so results drift apart at the extremes. For an average adult the gap is small. For a small child or a very large adult it grows.
Some sources prefer Haycock or Gehan and George for children, and Mosteller or DuBois for adults. This tool does not pick one for you. If a clinic gave you a formula name, look at that line.
BSA and Medication Doses
Some treatments, such as certain cancer drugs, are dosed per square meter. A care team picks the formula, checks the measurements, and decides whether to adjust the dose. Pharmacists often verify the final amount.
Do not use this page to set or change any medication dose. Ask your doctor or pharmacist about doses. Other body-size tools are nearby. Try the Lean Body Mass Calculator or the Ideal Weight Calculator. The BMR and TDEE Calculator covers daily energy needs.
To compare fat distribution, try the Waist to Hip Ratio Calculator. You can browse more in the health and fitness calculators hub.
Limitations and Assumptions
- The result is a general estimate. It is not a diagnosis, not medical advice, and not for drug dosing.
- Only metric units are accepted. There is no pound or inch input.
- Age and sex are not asked, and no formula is chosen for you.
- Height must be 30 to 250 cm and weight 2 to 500 kg. Anything else shows a message and N/A.
- A very odd pair inside those limits, such as 250 cm and 30 kg, still returns numbers.
- Results show two decimals. Rounding can differ slightly from clinic software.
FAQs About the Body Surface Area Calculator
What is body surface area?
It is the estimated outer surface of the body, in square meters. It is calculated from height and weight, not measured directly.
Which BSA formula does the tool use?
It shows four: Mosteller, DuBois, Haycock, and Gehan and George. The other three sit beside the headline result, so you can compare them.
Can I enter pounds and inches?
No. Height is in centimeters and weight is in kilograms. Convert first, using 2.54 cm per inch and about 2.2046 pounds per kilogram.
Can I use this to calculate a drug dose?
No. Treatment teams choose the formula and check the numbers. Ask your doctor or pharmacist about any dose. This page gives a general estimate only.
Can I use it for a child?
The math accepts child measurements, as the 100 cm and 16 kg row shows. Children have wide normal ranges, and the BMI card is not meaningful for them. A pediatrician should guide any decision.
Why is Mosteller shown first?
The tool's note says Mosteller leads because it is the simplest formula. It does not rank the four as more accurate. If an entry is invalid, the copy button shows Fix inputs and copies nothing.
This calculator gives general estimates only and is not medical advice. Reviewed for general accuracy by Prof. Dr. Khalil Mudassar, PhD.