BMI stands for "body mass index." The units for body mass index can be either kilograms per meters squared, or pounds per inches squared. The equations for either unit are below:
BMI = weight (kg) / height (m^2)
BMI = (mass (lb) / height (in^2)) x 703
There are also BMI calculators online that will calculate your BMI for you, such as the one found offered by the U.S. NIH.
BMI is one strategy to determine if person is of a healthy weight, and it is supposed that weight in a BMI height-to-weight ratio is an indicator of the presence or absence of health risks, for example, a risk of diabetes or heart attack. The CDC advises that BMI does not measure fatness but rather weight in relation to height and that people with the same BMI can have different levels of fatness.
a relatively high BMI can be the results of either high body fat or high lean body mass (muscle and bone). ("About Adult BMI," CDC)
These are important things to keep in mind when you take your own BMI measurement; BMI should be professionally assessed since the objective is to uncover health risks associated with weight. Please see the below ranges (given in kg/m^2):
Normal (healthy weight): 18.5-25
Moderately obese: 30-35
Severely obese: 35-40
Very severely obese: over 40
Please note that there are some exceptions to the rule. Some races have smaller skeletal frames. Their BMI ranges may run lower than these stated above. Athletes will have a higher BMI because of their muscle mass. Yet, their weight is healthy and doesn't indicate health risks.
If you are athletic, you are likely to be more muscular and have higher bone mineral density than a sedentary or non-athletic person, and that adds up to extra pounds. When you put your weight into the BMI equation, you may get a value greater than 25 percent ("What Is a Realistic BMI for Someone Athletic?" LiveStrong.com)