How to use the BMI calculator
Choose metric or US units, then enter your height and weight. Your body mass index appears instantly together with its weight category, the healthy weight range for your height and two related measures: BMI Prime (your BMI divided by 25, where anything above 1.0 is over the upper normal limit) and the ponderal index, which scales better for very tall or very short people. Everything is calculated in your browser – nothing you type is sent anywhere.
The BMI formula
BMI = 703 × weight (lb) ÷ height (in)²
For example, a person who is 1.75 m tall and weighs 75 kg has a BMI of 75 ÷ 3.0625 ≈ 24.5.
BMI categories for adults
| BMI | Category |
|---|---|
| Below 16 | Severe thinness |
| 16 – 17 | Moderate thinness |
| 17 – 18.5 | Mild thinness |
| 18.5 – 25 | Normal weight |
| 25 – 30 | Overweight |
| 30 – 35 | Obese class I |
| 35 – 40 | Obese class II |
| 40 and above | Obese class III |
These ranges follow the World Health Organization classification for adults aged 20 and over. Children and teenagers are assessed with age- and sex-specific percentiles instead.
Limitations of BMI
BMI is a quick screening tool, not a diagnosis. It does not distinguish muscle from fat, so athletes can register as overweight while being very lean. It also says nothing about where fat is stored – abdominal fat carries more health risk than fat on the hips. Older adults may have a normal BMI while carrying more body fat than younger people, and some ethnic groups face higher risk at lower BMI values. For a fuller picture, combine BMI with waist circumference, the body fat calculator and advice from a healthcare professional.
Worked example
Someone who is 5 ft 9 in (69 inches) tall and weighs 165 lb has a BMI of 703 × 165 ÷ 69² = 115,995 ÷ 4,761 ≈ 24.4, which sits near the top of the normal range. For that height, the healthy range of 18.5 to 24.9 corresponds to about 125 to 168 lb. Seeing your result as a range rather than a single target weight is usually more helpful and more realistic when setting goals.
Frequently asked questions
What is a healthy BMI?
For most adults a BMI between 18.5 and 24.9 is considered the normal or healthy range.
Is BMI accurate for athletes?
Not very. Muscle is dense, so muscular people can have a high BMI without excess fat. A body fat measurement is more useful for them.
Can I use this BMI calculator for children?
No. Children and teens need BMI-for-age percentile charts, because healthy body composition changes as they grow.
Do you store my height and weight?
No. The calculation runs entirely in your browser and nothing is sent to our server.
Last reviewed 2026-10-27. This bmi calculator is provided for general information; verify important decisions with a qualified professional.