How BMI is calculated
Body Mass Index divides your weight by the square of your height. It’s a quick screen that sorts most adults into standard weight categories.
- weight — body weight (kg)
- height — height in meters (cm ÷ 100)
More detail
What the categories mean
For adults the standard ranges are: below 18.5 underweight, 18.5–24.9 normal weight, 25–29.9 overweight, and 30 or above obese. The same thresholds are used worldwide.
Practical tip. A single reading matters less than the trend — weigh yourself about once a week at the same time of day. If you're muscular, older, or pregnant, check body fat % or waist size alongside BMI.
Frequently asked questions
What is a normal BMI range?
18.5–24.9 is classed as normal weight for adults worldwide. Below 18.5 is underweight, 25–29.9 overweight, and 30+ obese — enter your height and weight above to see your value and category.
Is BMI accurate for muscular people?
No. BMI only uses weight and height, so it can't tell muscle from fat — athletes and heavily muscled people are often flagged "overweight" despite low body fat. Body fat % or waist measurements are better for them.
What's a healthy weight range for my height?
The healthy-weight range output above converts the 18.5–24.9 normal BMI band into kilograms for your exact height, so you can see the full range rather than a single target number.