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Free BMI Calculator

Free BMI calculator. Enter your height and weight in metric or imperial units to get your Body Mass Index and see which BMI category you fall into.

Our free BMI calculator works out your Body Mass Index from your height and weight, tells you which BMI category you fall into, and shows where you sit on the BMI scale — in both metric and imperial units.

What is BMI?

Body Mass Index (BMI) is a number calculated from a person's weight and height. It is widely used as a screening tool to identify whether a person is underweight, normal weight, overweight, or obese. BMI is defined as weight in kilograms divided by height in metres squared (kg/m²).

BMI categories

BMI Category
Below 18.5Underweight
18.5 – 24.9Normal weight
25.0 – 29.9Overweight
30.0 and aboveObese

How to calculate BMI

Metric: BMI = weight (kg) ÷ height (m)². For example, a person who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.

Imperial: BMI = (weight (lbs) × 703) ÷ height (in)². For example, 154 lbs at 5 ft 9 in (69 in): (154 × 703) ÷ (69 × 69) = 22.7.

Limitations of BMI

BMI is a useful population-level screening tool, but it has limitations for individuals. It does not account for muscle mass, bone density, age, sex, or fat distribution. Athletes may have a high BMI due to muscle rather than fat. BMI should be used alongside other health indicators, not as a definitive measure of health. Always consult a healthcare professional for medical advice.

Frequently Asked Questions

What is BMI?
BMI (Body Mass Index) is a number calculated from your height and weight. It is used as a screening tool to categorize people as underweight, normal weight, overweight, or obese. The formula is weight (kg) ÷ height (m)².
What is a healthy BMI range?
For adults, a BMI between 18.5 and 24.9 is considered healthy. Under 18.5 is underweight, 25–29.9 is overweight, and 30 or above is classified as obese. These thresholds are the same for men and women.
Is BMI an accurate measure of health?
BMI is a useful population-level screening tool but has real limitations for individuals. It does not account for muscle mass, bone density, age, sex, or where fat is stored. Athletes often have a high BMI due to muscle, not fat. Use BMI alongside other health indicators and consult a healthcare professional for a complete picture.
How do I calculate BMI manually?
In metric units: divide your weight in kilograms by your height in metres squared. For example, 70 kg at 1.75 m: 70 ÷ (1.75 × 1.75) = 22.9. In imperial units: (weight in lbs × 703) ÷ height in inches².
Does BMI apply to children?
BMI for children and teenagers is calculated the same way but interpreted differently — using age- and sex-specific percentile charts rather than fixed thresholds. This calculator uses adult thresholds and is not suitable for people under 18.
Can I have a normal BMI and still have too much body fat?
Yes. This is sometimes called "normal weight obesity" or "skinny fat" — a person can have a normal BMI but a high body fat percentage and low muscle mass. For a more direct measure of body composition, use a body fat percentage calculator.

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