What does BMI mean?
BMI stands for body mass index. It is a person's weight in kilograms divided by the square of their height in meters, and the CDC lists named ranges for adults 20 and older. It is a number from two measurements, so it cannot see what the weight is made of and it is not a diagnosis.
Action level No action usually needed
- Why you are seeing it
- It appears on health forms, in fitness apps and in news stories about weight, usually as a single number such as 24.3.
- Why it matters
- It is a quick way to relate weight to height, and the ranges give the number a name. It is only a starting point for a conversation, because it cannot see what the weight is made of.
- What should I do?
- Work out the number from your own height and weight with the BMI Calculator.
- Read the category as a label for a range of numbers, not as a verdict about you.
- Ask a doctor what your number means for you, because they can look at much more than two measurements.
- A common misunderstanding
- A BMI category is not a diagnosis and it does not measure body fat.
How BMI is worked out
BMI is a person's weight in kilograms divided by the square of their height in meters. In US units the same value is 703 times the weight in pounds divided by the height in inches squared.
A simple example
A worked example
A person who weighs 160 pounds (72.6 kg) and is 5 feet 8 inches (1.727 m) tall: 72.6 / (1.727 x 1.727) = 72.6 / 2.983 = 24.3.
On the CDC adult ranges, 24.3 falls in the 18.5 to less than 25 range, which the CDC labels healthy weight.
The same person could be a different build with the same number, which is why the number alone says little.
The ranges the CDC lists for adults
| BMI | Category the CDC lists |
|---|---|
| Less than 18.5 | Underweight |
| 18.5 to less than 25 | Healthy weight |
| 25 to less than 30 | Overweight |
| 30 or greater | Obesity |
What the number leaves out
BMI uses only height and weight, so it cannot tell muscle from fat or know a person's build. The ranges above are the ones the CDC lists for adults 20 and older: this page does not give a category for anyone younger.
Try these tools
- BMI CalculatorCalculate BMI from height and weight in US or metric units, with its limits explained.
- BMI Range CalculatorTurn two BMI values into the weights they correspond to at your height. A mathematical range, not an ideal weight.
- Weight Change CalculatorSee the change between two weights as an amount, a percent and an average per week.