BMI Calculator
Calculate your Body Mass Index in metric or US units and see which weight category you fall into. Fast, free and completely private.
- Under 18.5 · Underweight
- 18.5–24.9 · Normal
- 25–29.9 · Overweight
- 30+ · Obese
What is BMI?
Body Mass Index (BMI) is a simple number that relates your weight to your height. It's widely used as a quick screening tool to sort people into broad weight categories — underweight, normal, overweight and obese — because it's easy to measure and correlates reasonably well with body fat across a population.
How to use this calculator
- Choose metric or US units.
- Enter your height and weight.
- Read your BMI and category — they update live as you type.
Understanding the result
BMI is a guide, not a complete picture of health. It doesn't distinguish muscle from fat or account for where fat is stored, so athletes and very muscular people can read as "overweight" despite being lean. Use it as a starting point and talk to a healthcare professional for personalized advice.
Frequently asked questions
How is BMI calculated?
BMI is your weight divided by the square of your height. In metric: kg ÷ m². In US units: 703 × lb ÷ in². The calculator does this automatically for whichever units you choose.
What are the BMI categories?
Under 18.5 is underweight, 18.5–24.9 is normal weight, 25–29.9 is overweight, and 30 or above is obese. These ranges are for adults aged 20 and over.
Is BMI accurate for everyone?
BMI is a useful general screening tool but it doesn't measure body fat directly. Very muscular people may have a high BMI without excess fat, and it isn't designed for children, pregnant people or the elderly. Treat it as a guide, not a diagnosis.
Is my data private?
Yes. Your height and weight are used only in your browser to compute the result. Nothing is uploaded or stored.