BMI Calculator — instant body mass index, free & private
Find your body mass index in seconds — metric or imperial, with no sign-up.
This tool runs entirely in your browser. Your files are never uploaded — they stay on your device.
- < 18.5 Underweight
- 18.5 – 24.9 Normal
- 25 – 29.9 Overweight
- ≥ 30 Obese
Body mass index (BMI) is a quick way to estimate whether your weight is in a healthy range for your height. This calculator works it out the moment you enter your numbers, switching freely between metric (kg, cm) and imperial (lb, ft + in) units.
Everything happens privately inside your browser — your height and weight are never sent to a server or saved anywhere. BMI is a general screening figure and does not account for muscle, bone or body composition, so treat it as a starting point and talk to a healthcare professional for personal advice.
How to use BMI Calculator
- Choose your preferred units — metric (kg, cm) or imperial (lb, ft and in).
- Enter your weight.
- Enter your height.
- Read your BMI value and weight category, which update instantly as you type.
Frequently asked questions
How is BMI calculated?
BMI is your weight in kilograms divided by the square of your height in metres (kg / m²). Imperial values are converted to metric first, so the result is identical either way.
What do the BMI categories mean?
Using the standard adult thresholds: under 18.5 is underweight, 18.5–24.9 is a normal weight, 25–29.9 is overweight, and 30 or above is in the obese range.
Are my height and weight uploaded or stored?
No. The whole calculation runs in your browser using plain JavaScript. Nothing you type is uploaded, logged or saved — close the tab and it is gone.
Is BMI accurate for everyone?
BMI is a useful general screening tool but it does not distinguish muscle from fat and is not designed for children, athletes or pregnancy. Use it as a guide, not a diagnosis.