BMI Calculator
How it works
BMI is weight divided by the square of height, in kilograms and metres: BMI = kg ÷ m². Pounds and inches are converted to those units first, so the same body gives the same index whichever way it is entered — 70 kg at 175 cm and 154.3 lb at 68.9 in are the same 22.9.
The index is then read against four bands. They are printed in tables as “18.5–24.9”, which is the same thing as “18.5 up to but not including 25” rounded to one decimal; a BMI of 24.97 sits in the second band here, even though it displays as 25.0.
| Category | BMI |
|---|---|
| Underweight | Under 18.5 |
| Normal | 18.5 to under 25 |
| Overweight | 25 to under 30 |
| Obese | 30 and above |
The weight range shown with the result is the other side of the same sum: the weights that would put your height at BMI 18.5 and at BMI 25. Because the index uses only two measurements, it carries no information about body composition or where weight is carried.
Daily energy use is a separate question from body mass index. The calorie calculator estimates it from weight, height, age, sex and activity level.
Frequently asked questions
Does BMI tell muscle from fat?
No. It is weight against height and nothing else, so a heavily muscled person and someone carrying the same weight as fat come out at the same number. It also says nothing about where weight sits on the body, which is why a waist measurement is often recorded next to it.
Which scale are these categories from?
The adult one — under 18.5, 18.5 to under 25, 25 to under 30, and 30 and above. Children and teenagers are read against age-and-sex percentile charts instead, so the same number means something different for them.
Is this medical advice?
No. BMI is a general screening figure worked out from two measurements; it is not a diagnosis or a health assessment. A clinician has the rest of the picture and can say what, if anything, the number means for you.