OnlineFreeToolBoxCalculators
BMI Calculator
About BMI Calculator
The BMI Calculator works out body mass index from weight and height. Enter weight in kilograms and height in centimetres and it shows a BMI number and a weight category, for example 24.2 — Healthy weight. BMI is a widely used screening number that relates weight to height, and it is often the first figure people check before looking at diet, exercise or health advice.
It is important to use the result for what it is: a general screening guide, not a diagnosis. Muscle, age, sex and body shape all affect what a healthy weight looks like for an individual, so treat the category as a starting point for a conversation, not a final verdict.
How to use BMI Calculator
- Enter your weight in kilograms in the “Weight (kg)” field.
- Enter your height in centimetres in the “Height (cm)” field.
- Press “Calculate BMI”.
- Read your BMI number and its category.
Why use BMI Calculator
A quick BMI check helps you put a number to a general sense of where you stand, and to track change over time when the same method is used each time.
- Simple inputs — only weight and height are needed.
- Clear categories — the number is shown with its weight category, not left unexplained.
- Useful for tracking — recheck with the same units to see whether the number is moving.
Your privacy
Your weight and height are entered in your browser only. They are not uploaded, stored or shared by this site.
Frequently asked questions
Is BMI a medical diagnosis?
No. BMI is a general screening number only; talk to a health professional for medical advice.
What BMI counts as healthy?
The usual healthy range is 18.5 to 24.9. Below that is underweight, 25 to 29.9 is overweight, and 30 and above is obese — the calculator shows the category for your result.
Should I worry about one BMI result?
Not on its own. BMI does not measure body fat, muscle or fitness, so use it as a general guide and speak to a health professional for personal advice.
Can children use this calculator?
This calculator uses the adult BMI scale. Children and teenagers are assessed with age- and sex-specific charts, so do not use this result for a child.
Why did my BMI change when only my height changed?
BMI depends on height squared, so even a small change in height has a noticeable effect on the result — double-check the height you entered.