The rough calculation — body mass index in short BMI — which is calculated by measuring your weight and height, is actually not a great measure of fitness when used on its own.
The BMI was invented in the 1830s, so it has probably outgrown its utility when you consider the following four points (according to obesity experts):
- It doesn’t give you a good estimate of how much body fat you're carrying around.
- It can differ drastically based solely on your gender. For example, a man and a woman with an identical body-fat percentage could have widely different BMIs.
- Just because you have a high BMI doesn't necessarily mean you're overweight. You can have a high BMI even if you have very little body fat, especially if you're male and very muscular.
- It doesn't take into account your waist circumference, which can be a good measure of your risk for certain diseases, including heart disease and type 2 diabetes.
- Regular doctor's visit.
- Measuring the circumference of your waist. Excess body fat — especially around your waist — has been strongly linked with specific health problems. Overweight people with large waists — more than 34.5 inches (88 cm) for women and more than 40 inches (102 cm) for men — are at a similar risk of developing diabetes as people who are clinically obese. The link is the strongest in female participants. (read the source)
- Calculating your body-fat percentage. This can be a bit tricky to do at home. In the US, personal trainers frequently use the skinfold method, which involves measuring the percentage of fat in various folds of skin on the body using skinfold calipers, to give you a rough estimate of your body-fat percentage.