BMI Calculator
Calculate your Body Mass Index in metric or imperial units and see your weight category instantly.
Calculate your BMI instantly
The BMI Calculator works out your Body Mass Index from your height and weight, in either metric or imperial units, and tells you which weight category you fall into. Enter your measurements and the result appears instantly, color-coded against the standard ranges. It runs entirely in your browser, so your data stays private.
What is BMI?
Body Mass Index is a simple ratio of weight to height — specifically weight in kilograms divided by height in metres squared. It is a widely used screening tool to categorize people as underweight, normal weight, overweight, or obese. Because it needs only two easy measurements, BMI is a quick, free way to get a general sense of whether your weight is in a healthy range for your height.
The BMI categories
| BMI range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
How to use it
- Choose metric (cm, kg) or imperial (ft/in, lb).
- Enter your height and weight.
- Read your BMI value and category instantly.
The limits of BMI
BMI is a useful screening tool, but it is not a complete picture of health. Because it only uses height and weight, it cannot tell muscle from fat — so very muscular people may register as "overweight" despite low body fat, while others may have a normal BMI but unhealthy fat levels. It also does not account for age, sex, or fat distribution. Treat your BMI as one data point and consult a healthcare professional for a full assessment.
Healthy weight beyond the number
- Waist measurement adds context about fat distribution and risk.
- Body fat percentage distinguishes muscle from fat.
- Activity and diet matter more than a single number.
- Trends over time are more meaningful than one reading.
Private and free
All calculations happen in your browser — your height and weight are never uploaded. The tool is completely free with no sign-up.
Frequently asked questions
How is BMI calculated?
BMI is your weight in kilograms divided by your height in metres squared. This tool also handles imperial units automatically.
What is a healthy BMI?
A BMI between 18.5 and 24.9 is generally considered the normal, healthy range for adults.
Is BMI accurate for athletes?
Not always. BMI cannot distinguish muscle from fat, so muscular people may have a high BMI despite low body fat.
Is my data private?
Yes. All calculations run in your browser and nothing is uploaded or stored.