What is BMI?
Body Mass Index (BMI) is a number calculated from a person's weight and height. BMI is a fairly reliable indicator of body fatness for most people. BMI does not measure body fat directly, but research has shown that BMI correlates to direct measures of body fat, such as underwater weighing and dual energy x-ray absorptiometry (DXA). BMI can be considered an alternative for direct measures of body fat. Additionally, BMI is an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems.
How is BMI used?
BMI is used as a screening tool to identify possible weight problems for adults. However, BMI is not a diagnostic tool. For example, a person may have a high BMI. However, to determine if excess weight is a health risk, a healthcare provider would need to perform further assessments. These assessments might include skinfold thickness measurements, evaluations of diet, physical activity, family history, and other appropriate health screenings.
How is BMI calculated and interpreted?
Calculation of BMI
BMI is calculated the same way for both adults and children. The calculation is based on the following formulas:
| Measurement Units |
Formula and Calculation |
| Pounds and inches |
Formula: weight (lb) / [height (in)]2 x 703
Calculate BMI by dividing weight in pounds (lbs) by height in inches (in) squared and multiplying by a conversion factor of 703.
Example: Weight = 150 lbs, Height = 5'5" (65")
Calculation: [150 ÷ (65)2] x 703 = 24.96 |
Interpretation of BMI for adults
For adults 20 years old and older, BMI is interpreted using standard weight status categories that are the same for all ages and for both men and women.
The standard weight status categories associated with BMI ranges for adults are shown in the following table.
|
BMI |
Weight Status |
| Below 18.5 |
Underweight |
| 18.5 – 24.9 |
Normal |
| 25.0 – 29.9 |
Overweight |
| 30.0 and Above |
Obese |
For example, here are the weight ranges, the corresponding BMI ranges, and the weight status categories for a sample height.
| Height |
Weight Range |
BMI |
Weight Status |
| 5' 9" |
124 lbs or less |
Below 18.5 |
Underweight |
| 125 lbs to 168 lbs |
18.5 to 24.9 |
Normal |
| 169 lbs to 202 lbs |
25.0 to 29.9 |
Overweight |
| 203 lbs or more |
30 or higher |
Obese |
What are the health consequences of overweight and obesity for adults?
The BMI ranges are based on the relationship between body weight and disease and death. Overweight and obese individuals are at increased risk for many diseases and health conditions, including the following:
- Hypertension
- Dyslipidemia (for example, high LDL cholesterol, low HDL cholesterol, or high levels of triglycerides)
- Type 2 diabetes
- Coronary heart disease
- Stroke
- Gallbladder disease
- Osteoarthritis
- Sleep apnea and respiratory problems
- Some cancers (endometrial, breast, and colon)