BMI Calculator
Enter your height and weight in metric or imperial units to see your BMI, your category and the healthy weight range for your height.
What BMI actually measures
Body Mass Index is a single number that relates your weight to your height. The formula is
simple: weight (kg) / height (m)^2. It was never designed to measure any one
person precisely - it was built to compare whole populations - but it is a quick, free way to
see roughly where your weight sits and whether it might be worth a closer look.
The formula, worked through
Say you are 1.75 m tall and weigh 70 kg. Square the height: 1.75 x 1.75 = 3.06. Divide:
70 / 3.06 = 22.9. That lands in the healthy band. In imperial units the sum is
703 x weight (lb) / height (in)^2, which gives the same answer - 703 is just the
conversion factor that lets you skip the metric step. The calculator above does the unit
conversion for you whichever way you enter your figures.
The standard categories
- Under 18.5 - underweight; worth checking you are eating enough.
- 18.5 to 24.9 - healthy weight for most adults.
- 25 to 29.9 - overweight.
- 30 and above - obese, split into further classes above 35 and 40.
Where BMI falls short
BMI cannot see inside you. A rugby player and a sedentary person of the same height and weight score identically, even though one is mostly muscle and the other mostly fat. It also reads high for people with a larger frame and can miss excess fat in older adults who have lost muscle. Waist measurement and body fat percentage tell a fuller story. If your number surprises you, use it as a prompt for a proper conversation with a GP rather than a verdict.
Planning changes off the back of your result? Pair this with the calorie calculator to find your daily energy needs, or use the percentage calculator to track weight change over time.