What BMI Is Normal?

Body mass index, or BMI, can be used an indicator of obesity and body fatness. The formula uses height and weight and is weight in kilograms divided by height in meters squared. Because height and weight are easily obtained, BMI can quickly indicate whether a person is overweight or obese. If you have a BMI indicative of overweight or obesity, you may need to lose weight to reduce your risk of diseases related to obesity.

BMI Values

Body mass index values are divided into five categories. If you have a BMI of less than 18.5, you are considered underweight. If you have a BMI between 18.5 and 24.9, you are considered to be at a normal weight. You are overweight if your BMI is between 25 and 29.9. A BMI of 30 and above is considered obese. The obese categories are divided into classes 1, 2 and 3.

Accuracy

There are more accurate methods than BMI for assessing body composition. Other methods include skinfold measurements, underwater weighing and dual-energy x-ray absorptiometry, or DEXA. Body mass index is used as an indicator of overweight and obesity because most clinicians do not have access to the more accurate testing methods. The National Heart Lung and Blood Institute suggests that BMI may overestimate body fat in athletes who are muscular, and underestimate body fat in elderly individuals who have lost some of their muscle mass.

Interpretation

If you have a BMI greater than 30, you should lose weight. If you are overweight and have other conditions such as high blood pressure, high cholesterol, high triglycerides or high blood glucose, you should lose weight. Being physically inactive and smoking cigarettes also puts you at an increased risk of developing certain diseases if you have a higher BMI. If your BMI is within the normal range, you should strive to maintain your weight.

Normal BMI Range

If you are overweight or obese, you should make changes to your lifestyle in order to lose weight and to maintain a weight within the normal BMI range. Start with small weight loss goals. The National Heart Lung and Blood Institute recommends a weight loss of 5 to 10 percent of your current body weight to reduce the risk of developing diseases such as heart disease and diabetes.