# Body Mass Index – What is BMI and How Is It Measured?

What Is Body Mass Index and How Is It Measured?

Body mass index, or BMI, is a measure of your weight compared to your height. It does not directly measure body fat, but it does tend to correlate well with measurement methods that do, such as skinfold thickness measurements, dual energy x-ray absorptiometry (DXA), and underwater weighing, to name a few. Generally, your BMI is a good indicator of whether you are at a healthy weight for your height, though it does have some limitations.

What BMI Indicates

BMI compares your weight to your height. The higher the number, the more weight you’re carrying around per inch of height. It indicates possible high body fatness, though it may not necessarily be spot on all the time.

Your body mass index can also indicate a likelihood of possible health complications due to excess body fat. While the two tend to correlate, further testing will be needed if you are found to have a high BMI.

Your BMI will place you in one of the following categories:

• 18.5 or below: underweight
• 18.5 to 24.9: normal weight
• 29 to 29.9: overweight
• 30 and over: obese

While these are generally accurate, remember that they are only general ranges. Determining whether your current weight is healthy or not will depend on further testing.

Calculating BMI

The measurement of body mass index is based on a formula that, in essence, divides your weight by your height. The exact formula is:

(Weight in pounds x 703) / (height in inches x height in inches)

For example, if someone who is 67 inches tall (or 5’7”) weighs 130 pounds, their formula would be:

(130 x 703) / (67 x 67)

Which comes out to:

91390 / 4489 = 20.36

Under the body mass index table, that person is at a healthy weight with a BMI of 20.36.

Limitations

The BMI table does have certain limitations. Factors that should be taken into account when interpreting the results include:

Age: Older adults tend to have more body fat than others.
Sex: Women tend to have more body fat than men.
Ethnic background: For example, African Americans will usually have less body fat than Caucasians.
Athleticism: An athlete’s weight will generally stem more from muscle than body fat, meaning a higher BMI will not necessarily be an indicator of higher body fat.

BMI is used as a preliminary screening tool to determine whether additional testing is needed, since these processes often require medical expertise and may be a bit costly. To learn more about healthy weight and BMI ranges, consult with a professional such as Dr. Malladi at Malladi Bariatrics and Advanced Surgery.