Understanding BMI: A Guide to Body Weight and Health
What is BMI?
Body Mass Index (BMI) is a calculation that uses your height and weight to categorize your body weight. Developed in the 19th century by the Belgian statistician Adolphe Quetelet, it remains one of the most commonly used tools for assessing weight. The formula is:
BMI = Weight in kilograms / (Height in meters)2
Learn more about the body mass index and its applications. Try our BMI Calculator to calculate yours today.
BMI Classifications and Risks
BMI is divided into the following categories:
- Underweight: BMI below 18.5
- Normal weight: BMI between 18.5 and 24.9
- Overweight: BMI between 25.0 and 29.9
- Obese: BMI of 30.0 or above
The American Institute for Cancer Research considers a BMI between 18.5 and 25 to be the ideal range for a healthy individual. However, BMI cut-off points are occasionally redefined and may differ by country. For instance, in 1998, the NIH adjusted the U.S. overweight threshold from 27 to 25, aligning it with WHO standards. This change reclassified about 30 million Americans from “ideal” weight to “overweight.”
Limitations of BMI
While BMI is useful, it has notable limitations:
- Fat Distribution: BMI does not account for fat location. Central obesity (“apple-shaped” fat around the abdomen) poses higher health risks than peripheral fat. Learn more about Body Composition Versus BMI.
- Muscle vs. Fat: Athletes with high muscle mass may be incorrectly classified as overweight or obese.
- Ethnic and Cultural Variations: BMI thresholds may not apply equally across all populations.
On its own, BMI cannot provide a full diagnosis. Other measures, such as waist circumference (better for predicting complications like insulin resistance), the skin fold test, or bioelectrical impedance analysis, offer a more comprehensive assessment.
Why BMI is Still Widely Used
BMI remains the most common metric in large-scale health studies because height and weight are easy to measure and record. This makes it valuable for public health analysis, even though it should not replace other diagnostic tools.
More Information on BMI and Health
For further reading, explore these resources:
Classification and Risks of Overweight and Obesity
Overweight and Obesity: What You Can Do
Body Composition Versus BMI