What is BMI?

If you're trying to lose weight -- or even if you aren't -- you've probably heard of BMI. It's actually an abbreviation for "body mass index," but most people just refer to it by the initials. Your body mass index is based on your height and your weight. This calculation gives you a number, which tells you whether you are underweight, normal (or healthy) weight, overweight, or obese.  Unlike some weight charts, the chart is the same for men and women. It's generally considered accurate, although people who are significantly more or less muscular than average may need to make some adjustments.

Why is BMI Important?

Knowing your body mass index important because it's an easy way for people to find out if they are at a healthy or unhealthy weight. A healthcare professional can determine your number, but it's also something that you can do for yourself at home.  When people see that their BMI indicates they are underweight, overweight, or obese, this knowledge may help motivate them to work towards having a healthier weight. This is especially important because of the obesity epidemic that has endangered the health of so many people. Obesity can be a significant factor in many serious diseases, including heart disease, diabetes, stroke, and high blood pressure. For some people, finding out that they have a high BMI can be a wake-up call that motivates them to make changes that can improve their health and extend their lifespans. When people are losing weight, their BMI numbers can show them how far they have progressed and how far they still need to go.  In this way, the BMI scale can be an ongoing motivating force. Fighting obesity is a problem that affects everyone, not only people who are currently overweight.  The director of the Centers for Disease Control and Prevention (the CDC) has said that obesity is the number one health problem in the U.S.

How Do You Measure Your BMI?

There are two ways to measure your body mass index. The easiest way is to use one of the many online BMI calculators, such as the one posted by the National Heart, Lung, and Blood Institute. For these calculators, you just type in  your height and weight, and you will get an instant result. Or you can calculate your BMI yourself, without needing an internet connection. To calculate your BMI manually --

1. Calculate your height in inches squared (that's  your height (in inches) times your height (in inches));
2. Divide your weight (in pounds) by your height in inches squared (from previous step);
3. Multiply the result by 703.

What Do the BMI Numbers Mean?

The numbers fall into four different categories. If your number is less than 18.5, you are considered underweight. If your number is 18.5 up to 24.9, congratulations, you have a normal or healthy weight. If your number is between 25 and 29.9, you are considered overweight. And if your number is 30 or more, you are considered obese.