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BMI Calculator
Enter your height and weight — metric or imperial — and get your BMI instantly, plus your weight category and the weight range that counts as healthy for your height. BMI is a screening measure, not a diagnosis: it does not distinguish muscle from fat.
Estimate for adults only — BMI is not designed for children, pregnant people, or athletes with very high muscle mass, and it is not medical advice. See the Calorie Calculator for daily energy needs.
How it works
BMI is weight divided by height squared: BMI = weight (kg) ÷ height (m)2. Imperial units convert first: pounds × 0.45359237 = kilograms, and inches × 0.0254 = metres. The World Health Organization categories are: under 18.5 underweight, 18.5–24.9 normal weight, 25–29.9 overweight, 30 and above obese. The healthy weight range for a height is the weight that gives a BMI of 18.5 at the low end and 24.9 at the high end. Worked example (metric): 175 cm, 70 kg → height 1.75 m, so BMI = 70 ÷ 1.752 = 70 ÷ 3.0625 = 22.9, Normal weight; healthy range = 18.5 × 3.0625 = 56.7 kg to 24.9 × 3.0625 = 76.3 kg. Worked example (imperial): 5 ft 9 in, 154 lb → 69 in × 0.0254 = 1.7526 m, 154 × 0.45359237 = 69.85 kg, so BMI = 69.85 ÷ 1.75262 = 22.7, Normal weight. Estimates only — BMI does not measure body fat directly and is not medical advice.
Frequently asked questions
What is a healthy BMI?
For most adults, 18.5 to 24.9 counts as the healthy range. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese, by World Health Organization cut-offs.
Why is BMI not the whole story?
BMI uses only height and weight, so it cannot tell muscle from fat. A muscular athlete can score as overweight with very low body fat, and an older adult can score normal while carrying excess fat. Treat it as a screening number, not a verdict.
Does BMI work for children?
No — children are assessed against age- and sex-specific BMI percentiles, not adult cut-offs, because their bodies change as they grow. This calculator is for adults.
How much weight do I need to lose to reach a healthy BMI?
The calculator shows it: the healthy range for your height, and how far above it you are. Losing even 5–10% of body weight brings real health benefits even before the range is reached.
Is the imperial formula different?
No — it is the same formula after unit conversion. The classic imperial shortcut, BMI = 703 × weight (lb) ÷ height (in)2, gives the same answer: 703 × 154 ÷ 692 = 22.7.