BMI Calculator
Calculate Body Mass Index & check health status
BMI Categories
| Category | BMI Range |
|---|---|
| Underweight | < 18.5 |
| Normal Weight | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obesity | 30 or greater |
Missing a tool?
Tell us what you'd like us to build next. We read every suggestion, and your email is optional.
What this calculator does
Body Mass Index (BMI) compares your weight to your height to give a single number. Health services use it as a quick screening measure for whether a person's weight is in a healthy range. This calculator works out your BMI as you type, places it on a color-coded scale, and tells you which adult category it falls into. It works in metric (centimeters and kilograms) or imperial (feet, inches and pounds), and nothing you enter leaves your device.
How to use it
- Choose Metric or Imperial at the top.
- Enter your height: centimeters, or feet and inches.
- Enter your weight in kilograms or pounds.
- Your BMI appears immediately. The marker on the bar shows where it sits, and the label shows its category.
The formula
In metric units, BMI is your weight in kilograms divided by your height in meters, squared:
BMI = weight (kg) ÷ height (m)²
In imperial units the same idea needs a conversion factor of 703:
BMI = 703 × weight (lb) ÷ height (in)²
A worked example
Someone who is 170 cm tall and weighs 65 kg has a height of 1.70 m. 1.70 squared is 2.89, and 65 divided by 2.89 is 22.5. That BMI of 22.5 falls in the healthy weight range. In imperial units, 5 ft 7 in is 67 inches and 65 kg is about 143 lb: 703 × 143 ÷ 67² gives the same result, about 22.4 (the small difference comes from rounding the conversion).
What the numbers mean
These are the adult categories (age 20 and over) used by the US Centers for Disease Control and Prevention:
| Category | BMI range |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5 to under 25 |
| Overweight | 25 to under 30 |
| Obesity | 30 or higher |
The CDC further divides obesity into class 1 (30 to under 35), class 2 (35 to under 40) and class 3 (40 or higher).
What BMI can't tell you
BMI is a screening measure, not a diagnosis. It doesn't measure body fat directly, and it can't tell muscle from fat. That's why it can misread some people:
- Athletes and very muscular people can have a BMI in the overweight range while carrying little body fat, because muscle is denser than fat.
- Older adults may have a healthy-looking BMI while having lost muscle and gained fat.
- Children and teens need different charts that account for age and sex. This calculator uses the adult categories only.
- During pregnancy, BMI isn't a useful measure of healthy weight.
As the CDC puts it, BMI should be considered with other factors when assessing an individual's health. Waist size, blood pressure, activity and family history all matter. If your result concerns you, talk to a doctor.
Frequently asked questions
Is BMI accurate for athletes?
Not always. Because muscle weighs more than the same volume of fat, a fit, muscular person can score as "overweight" without excess body fat.
Is the healthy range the same for men and women?
Yes, the adult categories are the same for everyone 20 and over. Body composition differs between people, which is one reason BMI is only a starting point.
Why is my result different on another site?
Usually because of rounding or units. This tool rounds to one decimal place and assigns the category from that rounded number, so a BMI shown as 25.0 is always labelled "Overweight".
What BMI should I aim for?
For most adults, a BMI from 18.5 to under 25 is considered a healthy weight. Your doctor can tell you what's right for you.
Do you store my height and weight?
No. The calculation happens in your browser, and nothing is sent to our servers.
Sources: CDC, Adult BMI Categories (reviewed by CDC March 19, 2024). Last reviewed on SuiteWebTools: October 2026.