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BMI Calculator
Your measurements
BMI is a screening tool, not a diagnosis. It does not measure body fat, muscle or overall health. This calculator is for general information only and is not medical advice.
Example: a 154 lb person who is 5 ft 9 in tall has a BMI of 22.7, in the healthy range.
Behind the numbers
How BMI is calculated
BMI divides your weight in kilograms by the square of your height in metres. In imperial units the same result comes from multiplying your weight in pounds by 703 and dividing by the square of your height in inches. The number is then sorted into one of four categories used for adults: underweight below 18.5, healthy from 18.5 to 24.9, overweight from 25 to 29.9, and obese at 30 or above.
154 lb ÷ 2.20462 = 69.9 kg, and 69 in × 0.0254 = 1.75 m. Then 69.9 ÷ 1.75² = 22.7, which is in the healthy range. In imperial units: 703 × 154 ÷ 69² = 22.7.
BMI categories for adults
Categories follow the standard adult BMI cutoffs used by the CDC and WHO.
A few comparisons
Example BMIs at 5 ft 9 in
| Weight | BMI | Category |
|---|---|---|
| 120 lb | 17.7 | Underweight |
| 154 lb | 22.7 | Healthy |
| 180 lb | 26.6 | Overweight |
| 210 lb | 31.0 | Obese |
Reading your BMI the right way.
BMI is a starting point, not a verdict. A single number cannot capture fitness, diet, sleep or family history — use it together with how you feel and what your clinician says.
Muscle weighs more than fat. If you lift weights, your BMI can read overweight while your body fat is low — in that case a body fat estimate tells you more.
Check your waist too. Where fat sits matters: a waist above 40 inches for men or 35 inches for women adds health risk even when BMI is in the healthy range.
Small changes move BMI slowly. At 5 ft 9 in, losing 5 lb lowers BMI by about 0.7 points, so steady habits beat crash diets for moving the number.
Good to know
Your BMI questions, answered.
What does BMI actually measure?
BMI is the ratio of your weight to the square of your height. It sorts adults into four weight categories — underweight, healthy, overweight and obese — and is used as a quick screening tool. It does not measure body fat directly.
Why is BMI not always accurate?
BMI cannot tell muscle from fat, so a muscular person can score as overweight while carrying little body fat. It also misses age-related muscle loss, and it does not account for where fat is stored. That is why it is a starting point, not a diagnosis.
What BMI range is considered healthy?
A BMI from 18.5 to 24.9 is considered the healthy range for most adults. For a person who is 5 ft 9 in tall, that works out to about 125 to 169 lb.
What is the difference between BMI and body fat percentage?
BMI uses only height and weight, while body fat percentage measures how much of your weight is fat versus lean tissue. Body fat percentage needs a separate method, such as calipers, a smart scale or a tape test like the Army body fat calculator.