BMI Calculator
Calculate your BMI from height and weight in metric or imperial units, with category and healthy weight range.
Enter your height and weight — your BMI is calculated as you type.
- Your BMI
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- Category
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- Healthy weight range
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- To reach it
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BMI is a rough screening number, not a diagnosis. It does not measure body fat directly and can misclassify very muscular people, older adults, pregnant people and children. Talk to a health professional before acting on it.
How it works
BMI (body mass index) is your weight divided by the square of your height:
BMI = kg ÷ m². In imperial units the same formula becomes
BMI = 703 × lb ÷ in². Type your height and weight and the calculator shows the
number immediately, together with the World Health Organization category it falls into —
underweight below 18.5, normal weight 18.5–24.9, overweight 25–29.9 and obesity from 30 up.
It also works backwards: from your height it calculates the healthy weight range (the weights that land you between a BMI of 18.5 and 24.9) and how many kilos or pounds separate you from it. Switch between metric and imperial at any time — the values you already entered are converted for you. Everything is computed in your browser with plain JavaScript: your height and weight are never uploaded, stored or sent anywhere, and there are no ads or sign-ups.
Frequently asked questions
How do you calculate BMI?
BMI is your weight in kilograms divided by the square of your height in metres: BMI = kg ÷ m². Someone who is 180 cm and 75 kg has a BMI of 75 ÷ 1.8² = 23.1. In imperial units the equivalent formula is BMI = 703 × pounds ÷ inches², so 5 ft 10 in and 165 lb also gives about 23.1. This calculator does the conversion for you in either unit system.
What is a healthy BMI range?
The World Health Organization classes a BMI below 18.5 as underweight, 18.5 to 24.9 as normal weight, 25 to 29.9 as overweight and 30 or above as obesity (class I 30–34.9, class II 35–39.9, class III 40+). The calculator also converts that 18.5–24.9 band back into an actual healthy weight range in kg or lb for your specific height.
Is BMI accurate for athletes, older adults and children?
Not always. BMI only compares weight to height, so it cannot tell muscle from fat: very muscular athletes often score as overweight while older adults who have lost muscle can score as healthy despite high body fat. It is also not valid for children and teenagers, who need age- and sex-specific percentile charts, or during pregnancy. Treat BMI as a screening number and discuss it with a health professional.