BMI Calculator
Calculate your Body Mass Index and get health insights. Supports both metric (kg/cm) and imperial (lbs/ft) units.
Enter your weight and height, then click Calculate BMI.
BMI Categories
What this BMI calculator does
Body Mass Index (BMI) is a single number calculated from your weight and height. This tool computes it and places the result on a colour-coded scale with four categories: Underweight, Normal Weight, Overweight and Obese. BMI is a screening measure for adults. It does not measure body fat directly, so treat the result as a starting point for a conversation with a clinician rather than a diagnosis.
The formula
BMI equals your weight in kilograms divided by your height in metres squared: BMI = kg / m². Imperial values are converted first. Pounds are multiplied by 0.453592 to get kilograms, and feet and inches are converted to total inches and then multiplied by 0.0254 to get metres. The calculator then applies the same formula, so both unit systems give the same answer for the same person.
How to use it
- Choose Metric (kg/cm) or Imperial (lbs/ft) at the top of the card. Switching units clears the current result.
- Enter your weight in kilograms or pounds.
- Enter your height in centimetres, or enter feet and inches in the two imperial fields.
- Press Calculate BMI. The result, its category and a short tip appear on the right, with a marker on the gauge.
Worked examples
Metric: a person weighing 70 kg and 175 cm tall has a height of 1.75 m. Squared, that is 3.0625, and 70 divided by 3.0625 is 22.9, which falls in the Normal Weight range.
Imperial: a person weighing 154 lbs and standing 5 ft 9 in tall converts to 69.85 kg and 1.7526 m. Squared, the height is 3.0719, and 69.85 divided by 3.0719 is 22.7. This is also Normal Weight.
Category ranges
- Underweight: below 18.5
- Normal Weight: 18.5 to 24.9
- Overweight: 25 to 29.9
- Obese: 30 and above
Limits and tips
- The calculator is designed for adults aged 18 and over. Children and teenagers are assessed against BMI-for-age charts instead.
- BMI cannot tell muscle from fat. Athletes and people with heavy muscle mass can land in the Overweight range while being lean.
- Pregnancy, older age and very short or very tall stature all change how the number should be read.
- Track the trend over several weeks rather than acting on a single reading.
- Cut-off points can differ between populations, so a healthcare professional may use different thresholds for you.
BMI Calculator – Frequently Asked Questions
What is BMI?
BMI (Body Mass Index) is a value derived from weight and height that provides a rough estimate of body fatness. It's calculated as weight (kg) divided by height squared (m²).
Is BMI accurate?
BMI is a useful screening tool but not a perfect measure of body fat or health. It doesn't account for muscle mass, bone density, or fat distribution. Athletes may have high BMI despite being healthy.
What BMI is considered healthy?
Generally: Underweight < 18.5, Normal 18.5–24.9, Overweight 25–29.9, Obese ≥ 30. These thresholds may vary by ethnicity and age group.
Should children use this calculator?
This calculator is designed for adults (18+). Children and teenagers have different BMI-for-age charts. Consult a pediatrician for children's BMI assessment.