BMI Calculator

What is BMI?

Body Mass Index (BMI) is a quick screening number that compares your weight to your height. Doctors and public-health organizations use it because it is simple, free and works for large groups of people. It is a starting point for a conversation about health, not a diagnosis.

How to use the calculator

1. Choose Metric (centimeters and kilograms) or Imperial (feet, inches and pounds).
2. Enter your height and weight. The result updates as you type.
3. Read your BMI, the category it falls into on the color gauge, and the healthy weight range for your height.
4. Optionally add your age, sex and activity level to get a rough daily calorie estimate for maintaining, losing or gaining weight.

The BMI formula

• Metric: BMI = weight (kg) ÷ height (m)²
• Imperial: BMI = 703 × weight (lb) ÷ height (in)²

For example, someone who is 175 cm tall and weighs 70 kg has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.

BMI categories for adults

Limits of BMI

BMI cannot tell muscle from fat, so a muscular athlete can land in the overweight range with very little body fat. It also ignores where fat is carried, and the health risks tied to a given BMI differ between ethnic groups. Some health bodies use lower cut-offs for people of South and East Asian descent. It is not designed for children and teens, who are assessed against growth charts for their age, and it is less reliable during pregnancy and for older adults.

Waist circumference, blood pressure, blood tests, fitness and family history all add context. If your result surprises you, or you are concerned about your weight, talk to a doctor or registered dietitian.

About the calorie estimate

If you enter your age, sex and activity level, the tool estimates your resting energy use with the Mifflin-St Jeor equation, then multiplies it by an activity factor to approximate daily calories for maintenance. Suggested targets for gradual loss or gain are shown as a guide only. Individual needs vary, so treat the numbers as a starting point and adjust based on real-world results.

Frequently asked questions

What is a healthy BMI?

For most adults, 18.5 to 24.9 is considered the normal range. The tool shows the weight range that corresponds to that band for your height.

Is my data stored?

Nothing is sent to a server. Your recent results are kept only in your own browser so you can compare them, and the Clear history button removes them.

Is this medical advice?

No. It is general information and cannot replace advice from a healthcare professional.