BMI Calculator
Enter your weight and height in kilograms and centimetres, or pounds, feet and inches, to see your adult BMI and its category. BMI is a screening measure, not a diagnosis.
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How do I calculate my BMI?
BMI is your weight in kilograms divided by your height in metres squared. Enter your weight and height in metric or imperial units and the calculator shows your BMI to one decimal and its adult category: under 18.5 is underweight, 18.5 to 24.9 healthy, 25 to 29.9 overweight, and 30 or more obesity.
- Choose metric (kilograms and centimetres) or imperial (pounds, feet and inches).
- Enter your weight and height. Decimals are fine, with a point or a comma.
- Read your BMI and its category, with the weight range that gives a BMI of 18.5 to 24.9 at your height.
Want to calculate BMI by hand, or see more worked examples? Read our guide: BMI by Hand: The Formula, Worked Examples and Adult Categories
Formulas & Methods
Metric
Example: 70 kg and 1.75 m: 70 ÷ 1.75² = 70 ÷ 3.0625 = 22.9
Imperial
Example: 154 lb and 5 ft 9 in (69 in): 703 × 154 ÷ 69² = 22.7
Key features
Metric or imperial
Enter kilograms and centimetres, or pounds, feet and inches. Conversions use the exact definitions of the pound and inch.
Adult categories
Shows the standard adult category for your BMI, from underweight to the three classes of obesity.
Healthy-weight range
Shows the weights that give a BMI of 18.5 to 24.9 at your height, for context.
Checks your input
Flags empty, zero, negative and implausible values, such as a height typed in metres instead of centimetres.
Adult BMI categories
These are the standard categories for adults. The World Health Organization, the CDC and the NHS all use the cut-offs 18.5, 25 and 30, and the CDC divides obesity into three classes. BMI is rounded to one decimal before it is classified.
- Below 18.5: underweight
- 18.5 to 24.9: healthy weight (WHO: normal weight)
- 25 to 29.9: overweight
- 30 to 34.9: obesity class 1
- 35 to 39.9: obesity class 2
- 40 or above: obesity class 3
What BMI can and can’t tell you
BMI is a quick screening measure for groups of people. It doesn’t measure body fat directly, so it can’t tell muscle from fat: an athlete can have a high BMI without excess fat. It also says nothing about where fat is stored, which matters for health.
It is interpreted differently for some people. For children and teenagers, BMI is compared with growth charts for their age and sex, which this calculator doesn’t do. It isn’t suitable during pregnancy. The NHS notes that people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds have a higher health risk at a lower BMI, and uses 23 and 27.5 as the thresholds for overweight and obesity.
This calculator gives information, not a diagnosis or medical advice. A doctor or nurse can explain what your result means for you.
Frequently Asked Questions
Can I enter my height in metres?
Enter centimetres: 175, not 1.75. A height under 3 is flagged as probably metres, and heights outside 50–275 cm or weights outside 10–650 kg are rejected as implausible rather than turned into a wrong BMI.
Is BMI accurate?
The calculation is exact, but BMI is only a screening measure. It doesn’t distinguish muscle from fat or show where fat is stored, so it is one indicator among several, not a diagnosis.
My BMI is 24.96. Why is it classed as overweight?
Because the category follows the displayed value. 24.96 is shown as 25.0, and 25.0 is the start of the overweight range, so the label always matches the number you see. A result this close to a cut-off is borderline either way.
Why does another calculator give a slightly different number?
Many calculators use the rounded 703 factor for pounds and inches, or round the height first. This one converts exactly and rounds the BMI to one decimal only at the end.
Is my weight stored or sent anywhere?
No. The calculation happens in your browser. Your weight, height and result are not stored and are never included in analytics.
Sources
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