There are more ways to measure a person's fitness than just stepping on a scale. Body mass index (BMI) and body fat are both measurements used to determine a person's level of personal fitness and gauge their risk for conditions such as heart disease and diabetes.

But what are the differences between these two measurements? Let's take a look.

Body Mass Index
Body mass index, or BMI, has been touted as the most accurate way to determine the effect of a person’s body weight on his or her health. BMI is used to assess risk for diseases, especially heart disease and diabetes. As BMI increases, so does the risk of developing these and other weight-related diseases, including stroke and some cancers.

BMI is a measurement of body fat based on height. The Centers for Disease Control and Prevention provide the following ranges for BMI values for adults:

Underweight: Less than 18.5
Recommended:6 to 24.9
Overweight:0 to 29.9
Obese: 30 or greater
The limitation of BMI is that this measurement does not distinguish fat from muscle. According to some research, more than half of Americans have a normal BMI but a high body fat percentage, which is known as normal weight obesity. A person who has normal weight obesity is just as unhealthy as someone with a high BMI.

Body Fat Percentage
Research on body fat percentage has improved in recent years, and in some cases, this measurement may provide a better picture of an individual’s risk of weight-related diseases than BMI. Body fat percentage distinguishes fat from muscle and calculates the percentage of body fat in the body. While BMI is a rough estimate of body fat, body fat percentage is a more accurate number.

Using body fat percentage, we might find that a highly trained athlete is overweight, according to the
BMI, but not overfat. Likewise, a person of normal weight on the BMI scales may still be overfat and at risk of weight-related diseases.

The American Council on Exercises provides the following ranges for body fat percentage for adults.

Women

Essential Fat:0-12 percent
Athletes:14-20 percent
Fitness: 21-24 percent
Acceptable:25-31 percent
Obese: 32 percent+
Men

Essential Fat:2-4 percent
Athletes:6-13 percent
Fitness:14-17 percent
Acceptable:18-25 percent
Obese:26 percent+
The downfall of body fat percentage as a measurement is that the methods of determining a person’s body fat percentage are not all equal, and the most accurate methods are not readily available. The two most common methods (skin fold measurement and bioelectrical impedance analysis) are often used in homes and gyms, but the accuracy of each varies and the error rates can be as high as eight percent. Other more accurate methods, such as X-ray analysis and water displacement, are much more complicated and not readily available.

In comparison to body fat percentage, BMI gives a good idea of an individual’s risk of weight-related diseases quickly and easily. If you work out regularly, body fat percentage should be calculated periodically to provide a more accurate picture of your health and fitness.

To learn your body fat rate, you can get yourself a BodyPedia Smart Scale, which has been proved to be the first accurate smart scale to be used at home. More than 10,000 tests comparing with medical devices show BodyPedia Smart Scales have around 97% correlation to the Gold Standard method (DXA).