BMI Calculator
Body mass index from height and weight, in metric or imperial units — with the standard categories and honest context about what BMI can and can't tell you.
Your BMI –
–
| Underweight | below 18.5 |
| Normal range | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obesity | 30 and above |
BMI is a population-level screening measure for adults, not a diagnosis. It can't distinguish muscle from fat and doesn't apply to children or during pregnancy. For questions about your health, talk to a doctor.
How BMI is calculated
BMI is weight in kilograms divided by height in meters squared; the imperial formula multiplies pounds over inches squared by 703. Both give the same number — a rough ratio of weight to height used for population statistics since the 19th century.
Pick your units
Metric or imperial — the calculator converts internally, so both are exact.
Enter height and weight
The BMI and its standard category update live as you type.
Read it in context
The category table shows where the number sits — and the notes explain its real limitations.
What BMI can and cannot tell you
BMI is useful for what it was built for: comparing large groups with one simple number. For an individual it's much blunter. It can't tell muscle from fat — athletes routinely score "overweight" while being lean — it ignores where weight is carried, and typical values shift with age, sex and ethnicity. Health is also more than a weight ratio: blood pressure, fitness, sleep and lab values all matter. So treat the number as one data point among many, and bring questions about it to a healthcare professional rather than a calculator.
Frequently asked questions
How is BMI calculated?
BMI = weight in kilograms divided by height in meters squared. In imperial units: weight in pounds divided by height in inches squared, multiplied by 703. This calculator handles both.
What are the standard BMI categories?
The WHO ranges for adults: below 18.5 underweight, 18.5–24.9 normal range, 25–29.9 overweight, 30 and above obesity. These are population-level screening ranges, not individual diagnoses.
What are the limitations of BMI?
BMI can't distinguish muscle from fat, so muscular people can score "overweight" while being lean, and it doesn't reflect where fat is stored. Age, sex and ethnicity also shift what's typical. It's a rough screening number, not a health verdict.
Does BMI apply to children or during pregnancy?
Not in this adult form. Children and teens use age- and sex-specific percentile charts, and BMI isn't a meaningful measure during pregnancy. For those cases, and for any health concern, talk to a doctor.