BMI Formula
The metric BMI formula
BMI means body mass index. The metric formula is weight in kg / height in meters squared. For example, 70 kg and 1.75 m gives 70 / (1.75 * 1.75) = 22.9.
The imperial BMI formula
When using pounds and inches, multiply by 703: BMI = weight in pounds * 703 / height in inches squared. The extra multiplier converts imperial units into the same BMI scale.
Adult BMI categories
The CDC describes adult BMI as a screening measure, not a diagnosis. For adults 20 and older, its categories are underweight below 18.5, healthy weight from 18.5 to less than 25, overweight from 25 to less than 30, and obesity at 30 or greater.
- Underweight: below 18.5
- Healthy weight: 18.5 to less than 25
- Overweight: 25 to less than 30
- Obesity: 30 or greater
What BMI does not show
BMI does not separate muscle, bone, water, and body fat. It also does not replace medical history, waist circumference, lab results, or a clinician's judgment. Athletes, older adults, pregnant people, and children may need different context.
Use the calculator
Open the BMI Calculator, choose metric or imperial units, and enter height and weight. Use the result as a general screening number, not as medical advice. For health questions, talk with a qualified healthcare professional.
Try the BMI Calculator →Calculate your Body Mass Index (BMI) in metric (kg, cm) or imperial (lb, in) and see your WHO category. Free, instant, no signup.Frequently asked questions
Is BMI a diagnosis?
No. The CDC describes BMI as a screening measure that should be considered with other health factors.
Is this BMI guide for children?
No. Adult BMI categories are for adults. Children and teens use age- and sex-specific percentiles.
Where do the adult BMI categories come from?
The categories match CDC adult BMI guidance for adults 20 and older.