What's the difference between BMI (body mass index) and body fat percentage?

Question

How are these two things different, and what's considered a healthy range for both?

I took a body fat percentage test, got only 16.2%, but is that the same as my BMI?

Answer 1

BMI is a simple ratio of height and weight. For average proportioned people it gives a reasonable guess at whether they are over weight or not.

However, for bodybuilders the BMI doesn't work at all. When Arnold won Mr Universe, his BMI rated him as being "morbidly obese".

The BMI is for coach potatoes. If you actually get some degree of exercise, you might be better off using skinfold calipers to determine your body fat percentage. Of course, even skinfold tests will vary widely depending upon how many sites you test. There are different calculations for 3-site, 4-site, 7-site and 9-site. I plug in the numbers and my bodyfat comes to 12% up to 18% depending on which formula I use. That is a considerable varience.

There is also hydrostatic testing where they take your weight under water. Muscle sinks and fat floats. But it depends on how well you can expel all the air in you. So if you have problems exhaling all the air in your lungs, or if you are tending to be flautulent and don't have all of that out, or if you are overly hydrated it will tend to give you a higher fat percentage than you actually have. My hydrostatic test results say I am at 22% body fat. (I like that 12% number with the 9-site skinfold formula much better.)

Answer 2

They should be close. BMI is a ratio used on a graph to put you on a percentile with the rest of the world. Body fat % is the actual amount of fat YOU have in YOU. Men range from 5-18% for the healthy male, anything over 25% is clinically obese. For women it is 12-28%, anything over 30% is clinically obese.