In this article (4 sections)
How is BMI Calculated?
The formula is weight in kg ÷ (height in meters × height in meters).
A calculation example: 78 / (1.72 x 1.72) = 26.4.
For US units, use weight in pounds / height in inches squared x 703. For example, 172 lb and 68 in gives 172 / (68 x 68) x 703 = about 26.1. This is a separate example, not an exact conversion of the metric example.
What are the adult BMI categories?
The CDC categories apply to adults age 20 and older:
| BMI | Screening category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to below 25 | Healthy weight |
| 25 to below 30 | Overweight |
| 30 or above | Obesity |
The names describe screening ranges. They do not diagnose health, nutritional adequacy, muscle mass or fat distribution. Children and teens need age-specific assessment rather than this adult table.
What Can BMI Be Used For?
BMI is used as an initial screening measure for adults. It does not indicate how much of the weight is muscle or fat, or how the fat is distributed. A professional assessment therefore also includes other information. See NIDDK's guide on weight assessment.
Is BMI a Calorie Measure?
No. BMI does not include age or activity level and does not indicate how much energy you use per day. The calorie needs calculator explains the separate calculation of energy expenditure.
Do not use adult BMI thresholds for children. Consult a healthcare professional if you want an assessment of your own weight and health. The article does not provide a diagnosis or recommend a weight loss target.