How to use the BMI calculator
- Choose imperial (feet, inches, pounds) or metric (centimeters, kilograms).
- Enter your height and weight. Decimal values like 5 ft 7.5 in or 72.4 kg are fine.
- Press Calculate to see your BMI to one decimal place with its category label.
This calculator uses the adult categories for people aged 20 and over. Children and teens are assessed with age- and sex-specific BMI percentiles instead, which this tool doesn't calculate.
How it's calculated
Imperial: BMI = 703 × weight (lb) ÷ height (in)²
| BMI | CDC adult category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obesity |
The factor 703 converts pounds per square inch into the metric kg/m² scale, so both unit systems give the same BMI for the same person.
Worked example
Someone who is 5 ft 10 in (70 inches) and weighs 170 lb has a BMI of 703 × 170 ÷ 70² = 703 × 170 ÷ 4,900 ≈ 24.4, which falls in the healthy weight range.
In metric, 178 cm and 77 kg gives 77 ÷ 1.78² = 77 ÷ 3.1684 ≈ 24.3.
FAQ
What is a healthy BMI for adults?
The CDC classes an adult BMI from 18.5 to 24.9 as healthy weight. BMI is a screening measure, so a clinician may look at other factors too.
Is BMI accurate for athletes?
Not always. BMI can't tell muscle from fat, so very muscular people may be labeled overweight despite low body fat.
Can I use this BMI calculator for children?
No. Children and teens aged 2 to 19 are assessed with BMI-for-age percentiles, which depend on age and sex. This tool uses adult categories.