BMI Calculator
Body Mass Index is a quick screen for whether your weight is in a healthy range for your height. This calculator works in both metric and imperial units and shows the CDC adult weight category your BMI falls into.
How to use the BMI Calculator
- Enter your numbers in the BMI Calculator above.
- Press the Calculate BMI button to see the result.
- To try other numbers, change any value and press the button again.
The BMI formula
BMI = weight (kg) / height (m)²
In imperial units, BMI = (weight in lb / height in in²) × 703. BMI is unitless and applies to adults aged 20+. The calculator uses the CDC's adult categories. Under 18.5 is underweight, 18.5 or more but under 25 is normal weight, 25 or more but under 30 is overweight, and 30 or more is obese. The calculator rounds BMI to two decimals and reads the category from that rounded number, so the number and the category always agree. A BMI of 29.95 is still overweight. A BMI of 29.995 shows as 30 and counts as obese.
Worked example
An adult who is 1.75 m tall and weighs 70 kg has a BMI of 70 / (1.75 × 1.75) ≈ 22.86, within the normal range. A 5'9", 180 lb adult has BMI = (180 / 69²) × 703 ≈ 26.58, in the overweight range.
Frequently asked questions
What is a healthy BMI for adults?
The CDC counts a BMI of 18.5 or more but under 25 as a healthy weight for adults. Under 18.5 is underweight, 25 or more but under 30 is overweight, and 30 or more is obesity.
Is BMI accurate for athletes?
BMI can overestimate body fat in muscular individuals because muscle is denser than fat. Athletes and bodybuilders with high muscle mass may have a BMI in the overweight range despite low body fat. Use a body fat or lean body mass calculator for a fuller picture.
Does BMI work for children?
Adult BMI categories do not apply to children and teens. For people under 20, BMI is interpreted using age- and sex-specific percentile charts from the CDC.
What are the limitations of BMI?
BMI is a screening tool, not a diagnostic. It does not measure body composition, fat distribution, or muscle mass, and it can misclassify athletic or elderly people. Pair it with body fat percentage or waist-to-hip ratio for a complete view.