What is a Body Mass Index Chart?

Lainie Petersen

Body mass index, also known as BMI, is a number that, for most people, accurately represents their percentage of body fat. While there are several methods for measuring body fat, a body mass index chart is an easy and inexpensive way for adults and children to determine if they are at a healthy body weight. The chart simply uses a person's height and weight to calculate a body fat percentage using a standardized formula.

Using a body mass index chart is simple. Many charts take the form of a grid with height measurements on the left side and weights across the top. A person, or their doctor, just needs to find both their height and weight on the grid, which will then point to their body mass index number. A body mass index under 18.5 is underweight, between 18.5-24.9 is normal, 25-29.9 is overweight, and a body mass index over 30 is considered obese.

There are different body mass index charts for men, women and children, each scaled to the average height and weights of each gender and age group. The formula for determining body mass index depends on the measurement system being used. To determine a percentage with metric weights, the body mass index chart will show the results of body weight in kilograms, which is then divided by the individual’s height in meters. The resulting number is then squared. In countries where pounds and inches are used, the percentage is determined by dividing pounds of weight by the individual’s height in inches. This number is then squared and multiplied by 703. This formula is used for all three body mass index charts.

The whole notion of body mass index has been criticized by some within the medical and fitness communities. Some argue that a body mass index chart doesn't work well for fitness buffs or serious athletes with a high percentage of lean muscle. This is because the body mass index doesn't actually measure an individual's body fat, but instead estimates the percentage of body fat based on a mathematical formula.

Another criticism is that some health professionals place too much emphasis on the percentage without considering other factors, such as genetics, lifestyle habits, stress, and previous medical history. The Centers For Disease Control in the United States does acknowledge these shortcomings and notes that the body mass index chart should not be the sole criteria used in determining whether someone is at a healthy body weight or is at risk for disease.