What is BMI?
Body Mass Index (BMI) is a single number that relates weight to height. It is widely used but does not measure muscle, bone, or where fat is stored, so it is not a full picture of health.
How is it calculated?
The usual definition is BMI = weight (kg) ÷ height (m)². On this calculator you can enter height in centimeters and weight in kilograms—we convert to meters and kilograms internally. If you choose ft/in and pounds, those are converted the same way before the formula is applied.
Common ranges (WHO adults)
Roughly: under 18.5 is underweight; 18.5 to under 25 is normal; 25 to under 30 is overweight; 30 and above is the obesity range. Interpretation can vary with age, ethnicity, pregnancy, and athletic build.
What if it is too low?
A low BMI can reflect nutrition, muscle mass, or illness, among other causes. Seek professional advice if you have rapid weight loss or symptoms like fatigue or dizziness.
What if it is high?
Higher BMI categories are associated with greater metabolic risk over time. Use them as a prompt to review diet, activity, and sleep—and consider waist circumference or clinical tests for a fuller view.
How to use this page
Korean uses centimeters and kilograms by default; English uses feet/inches and pounds—common everyday pairs in each region. Enter your numbers and tap Calculate to see BMI, category, and the scale marker. You can switch units anytime; internally everything converts to meters and kilograms before the same formula runs. Your inputs are calculated only in this browser and are not sent to a server.
Units and language
Korea and many countries use centimeters and kilograms day to day. In the US, height is often given in feet and inches and weight in pounds. When you change the site language we adjust the default units to match common practice—not to lock you in, so pick another unit from the menus whenever you like.