How to use the BMI and body fat calculator
- Choose the units (cm·kg or ft·in·lb), sex, age and category standard, then enter your height and weight.
- Your BMI, its category, a healthy weight range and body fat estimates appear at once.
- For a more detailed body fat estimate, open "Also estimate body fat from circumferences" and enter waist and neck measurements (and hip for women).
What is BMI?
BMI (body mass index) is weight divided by the square of height, a simple measure of whether weight is high or low for your height. It is easy to calculate and widely used in health checkups. The Asia-Pacific standard classes a BMI under 18.5 as underweight, 18.5 to 22.9 as normal, 23 to 24.9 as at risk (overweight), 25 to 29.9 as obese class I, 30 to 34.9 as class II and 35 or more as class III. The WHO international standard treats 18.5 to 24.9 as normal, 25 to 29.9 as overweight and 30 or more as obese.
How body fat is estimated
This calculator offers two estimates. The first uses BMI, age and sex: body fat % = 1.20 × BMI + 0.23 × age − 10.8 × sex (male 1, female 0) − 5.4. The second is the circumference method used by the US Navy, which puts waist, neck (and hip for women) and height into a logarithmic formula. Both are statistical formulas built on average people, so the error grows if you have a lot of muscle or an unusual build. The reference ranges shown are simplified, commonly cited ranges and are not diagnostic criteria.
Things to know
- BMI cannot tell muscle from fat. Someone with a lot of muscle, such as an athlete, can have a high BMI and low body fat.
- Interpretation can differ for older adults, very short or tall people, and during pregnancy.
- Under age 18, adult categories are not used; growth charts are used instead.
- Abdominal fat matters too. The Korean Society for the Study of Obesity treats a waist of 90 cm or more for men and 85 cm or more for women as abdominal obesity.
- Do not judge your health from a single BMI number; look at eating habits, activity and results such as blood pressure and blood sugar together.
FAQ
How is BMI calculated?
Divide weight in kilograms by the square of height in meters. For example, 170 cm and 65 kg gives 65 ÷ (1.7 × 1.7) = about 22.5.
How do the Asia-Pacific and WHO standards differ?
Studies suggest people of Asian descent face higher metabolic risk at lower BMI values, so the Asia-Pacific standard counts 23 as "at risk" and 25 as obese. The WHO international standard uses 25 for overweight and 30 for obese. This calculator lets you choose either.
How accurate is the body fat estimate?
Both the BMI-and-age method and the circumference method are statistical estimates, so they can differ from your real body fat by several percentage points. For an accurate number use a body composition scan or a medical test.
Notes & limitations
This calculator is for reference only and is not a medical diagnosis or treatment advice. If you plan a big change in weight or diet, or are worried about your health, talk to a doctor or dietitian. The values you enter are never sent to a server and are calculated only inside your browser.