Body mass index, or BMI, is a calculation used by doctors and fitness professionals to help determine and predict obesity and overweight. BMI is used in concert with other diagnostic tests and observations, such as diet assessments and skin fold thickness tests. Because body fat is linked to an increased risk of a number of diseases, such as diabetes, cancer and heart disease, understanding your BMI can help you make a plan to improve your overall health.
Body Mass Index
Your body mass index, calculated from your height and weight, indicates your body's level of fatness. Calculating BMI is not as accurate as other, more direct methods of measuring body fatness, such as dual energy X-ray absorptiometry or underwater weighing. However, BMI gives enough of a picture of body fatness to help determine obesity and estimate the likelihood of future weight-related health problems.
Ideal BMI
The ideal BMI is between 18.5 and 24.9, says the Centers for Disease Control and Prevention. A BMI of less than 18.5 indicates that the person is underweight. A BMI of 25.0 to 29.9 indicates obesity. A BMI of 30 or higher means the person is obese. However, other factors may affect the interpretation of BMI in relation to appropriate weight. Women tend to have a higher percentage of body fat than men of the same BMI. Body fat also increases with age. Athletes may have a higher BMI due to an increase in muscle weight, not body fat.
Calculating BMI
To calculate BMI, divide your weight in pounds by your height in inches squared and multiply the result by 703. If using the metric system, divide your weight in kilograms by your height in meters squared. You need not multiply by an additional conversion factor when calculating BMI using the metric system. BMI calculations for children use a different system, based on percentiles of weight and height, because children grow at different rates throughout childhood and adolescence.
Achieving a Better BMI
Diet and exercise are the best ways to improve your BMI and overall health. If your BMI indicates that you're overweight or obese, cutting back on calories and instituting a program of regular physical activity with aerobic or cardiovascular exercise can help you lose weight and reduce your BMI. You should aim for at least 30 minutes of exercise on most days of the week. People with a low BMI may need to consume more calorie-dense healthy foods such as avocados, olive oil, dried fruits and fatty fish. Strength training may improve BMI by building muscle.
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