BMI Calculator
Calculate your Body Mass Index and find out which weight category you fall into.
Did this tool work for you?
How to use this calculator
Divide your weight in kilograms by the square of your height in metres.
- 1
Enter your weight in kilograms.
- 2
Enter your height in centimetres.
- 3
Your BMI and weight category appear instantly.
- 4
The ideal weight range shows the healthy BMI span for your height.
Frequently asked questions
Which categories does the calculator use?
Four bands, applied to the unrounded BMI: below 18.5 is Underweight, 18.5 up to but not including 25 is Normal weight, 25 up to but not including 30 is Overweight, and 30 or above is Obese. There are no sub-classes of obesity and no separate thresholds for age, sex or ethnicity.
My BMI shows 25.0 but the category says Normal weight. Why?
The label is chosen from the exact value and the display is rounded to one decimal. A 175 cm person weighing 76.5 kg has a BMI of 24.98, which prints as 25.0 but is still below the 25 cut-off, so it reads Normal weight.
How is the “ideal weight range” worked out?
It is the weight at which your height produces a BMI of 18.5, up to the weight that produces 24.9, using height in metres squared. At 175 cm that is 56.7 to 76.3 kg. It is a BMI band expressed in kilograms, not a target, and the 24.9 upper limit sits just under the 25 cut-off, so the two can differ by a few hundred grams.
Can I enter pounds, feet or inches?
No, the inputs are kilograms and centimetres only. Convert first: divide pounds by 2.205 for kilograms and multiply inches by 2.54 for centimetres. A 5 ft 9 in person is about 175 cm.
What input does it reject?
A weight or height that is zero, negative or not a number returns an error rather than an infinite or nonsense BMI. It does not stop you entering very large or very small values, so a typo like 1750 cm for 175 cm will produce a very low BMI instead of a warning.
Does BMI work for children, pregnancy or athletes?
The calculator applies the adult bands to any entry. It does not use growth charts for children, adjust for pregnancy, or know about muscle, so a muscular person can land in a heavier band. For those groups a doctor or nurse uses different methods.
Is a result outside the Normal band a diagnosis?
No. BMI is height and weight arithmetic and says nothing about fat distribution, fitness or blood results. This is general information, not medical advice; a clinician can look at the wider picture.
BMI — what the calculator computes and how the bands fall
The calculation in plain terms
Your height in centimetres is turned into metres, squared, and used to divide your weight in kilograms. The result is shown to one decimal place and matched against four bands. The calculator also returns the weight range that would put someone of your height between BMI 18.5 and 24.9, so you can see the span in kilograms rather than index points. Nothing about age, sex or body composition enters the sum, and the category is decided before rounding, so the printed value and the label can occasionally look one step apart.
Worked examples
These came from running the calculator. A 70 kg person at 175 cm has a BMI of 22.9, Normal weight, with a range of 56.7 to 76.3 kg. A 95 kg person at 180 cm has 29.3, which is Overweight, against a range of 59.9 to 80.7 kg. A 52 kg person at 165 cm has 19.1 (Normal weight, range 50.4 to 67.8). A 45 kg person at 170 cm has 15.6 (Underweight), and a 100 kg person at 170 cm has 34.6 (Obese).
What the band edges mean in kilograms
The same BMI band covers a wide weight span that grows with height, as the table below shows.
| Height | Lower weight | Upper weight |
|---|---|---|
| 160 cm | 47.4 kg | 63.7 kg |
| 165 cm | 50.4 kg | 67.8 kg |
| 170 cm | 53.5 kg | 72.0 kg |
| 175 cm | 56.7 kg | 76.3 kg |
| 180 cm | 59.9 kg | 80.7 kg |
Why height is squared
Weight does not rise in direct proportion to height, so the formula divides by height squared rather than height. It is a convention rather than a law of body shape, so two people of very different build can share an index. A shift of one centimetre or one kilogram in the inputs is enough to change the first decimal place.
Where BMI stops being useful
Because the number ignores muscle, bone density and where fat sits, it works best as a quick screen across a population or for following your own trend with the same scale. It does not predict how you feel or any particular test result. Waist measurement, body fat estimates and a conversation with a health professional add detail. This page offers general information, not medical advice.
Learn more from an authoritative source:
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →