About BMI Calculator
BMI Calculator converts a weight and a height into a Body Mass Index and places the result in a standard category. The arithmetic is weight in kilograms divided by height in metres squared, and the category boundaries follow the widely used World Health Organization cut-offs: below 18.5 is underweight, 18.5 to 24.9 is normal weight, 25 to 29.9 is overweight, and 30 and above is obese.
Because the thresholds are applied to the rounded index, the output shows the category alongside the one-decimal BMI figure, so you can see both the number and which side of a boundary it fell on. Heights are entered in centimetres and converted internally, which means you do not have to do that step yourself and risk a decimal error.
Two limits are worth stating plainly. BMI uses only height and weight, so it cannot distinguish muscle mass from fat — a well-trained athlete can land in the overweight band at a low body-fat percentage. It is also not designed for children, whose healthy ranges are age- and sex-specific percentile charts, nor for use during pregnancy. Read the number as a population-level screening figure, not as a diagnosis.
How to use BMI Calculator
- 1 Enter your weight in kilograms.
- 2 Enter your height in centimetres.
- 3 Read the BMI to one decimal place together with its category.
Frequently asked questions
Can it take pounds and feet?
Not directly. The fields are kilograms and centimetres, so weights and heights in imperial units need converting first. Mixing a pound figure into the weight field would produce a wildly wrong index without any error being raised.
Why does my category differ from what my doctor said?
Clinical assessment uses more than height and weight — waist circumference, body composition and medical history all play a part. BMI is a fast screening ratio, and the category it produces is one input to that judgement, not a substitute for it.
Does it work for children or teenagers?
No. Healthy BMI ranges for under-20s are read from growth charts indexed by age and sex, because body composition changes rapidly during development. The adult cut-offs applied here would misclassify them.
Why is the BMI shown to one decimal place?
That is the conventional presentation and it is enough to see which band you are in. Showing more digits would suggest a precision that two self-reported measurements cannot deliver.
Free, online, and private
Free to use
BMI Calculator is completely free. There is no account to create, no login, and no hidden charge or usage limit.
Runs online in your browser
It is a free online tool that runs entirely in your browser. Nothing to download or install — open the page and start using it right away.
Your data stays private
All processing happens locally on your device. Your input is never uploaded, stored, or tracked, so it never leaves your browser.
How BMI Calculator behaves in detail
These are the specifics of this implementation — the exact ranges, defaults and fixed settings you are working with.
| Parameter | Value |
|---|---|
| Formula | weight in kg ÷ (height in metres)² |
| Inputs | weight in kilograms, height in centimetres |
| Defaults | 70 kg and 175 cm |
| Result precision | one decimal place, with a category label |
| Category thresholds | below 18.5 underweight · 18.5–24.9 normal · 25–29.9 overweight · 30 and above obese |
Compiled from the implementation of this tool and checked against it by itoolnet.
What BMI Calculator does not do
Knowing the edges of a tool saves more time than another list of its features. These are the cases where it will not do what you might expect.
- BMI is a ratio of weight to height and nothing else. It does not distinguish muscle from fat, so a muscular athlete can read as overweight while carrying very little fat, and it takes no account of age, sex, bone density or body composition.
- Input units are metric only. Feet and inches, and pounds, have to be converted first — this tool offers no imperial entry.
Tested and documented by itoolnet, the team that builds and maintains this site.