How to Calculate BMI Using Factors & Average BMI for Age

Body mass index, or BMI, is calculated using a person's height and weight. BMI is typically used to determine body fat percentage and compare it to national averages, according to the Centers for Disease Control and Prevention (CDC). Your BMI number can indicate whether you are an average weight for your age and height, or whether you are under- or overweight. The TeensHealth website reports that in children and teens, BMI can determine whether the child or teen is at risk for becoming overweight or obese later in life. BMI can be calculated using an online tool, such as the one used on the CDC website, or you can calculate it yourself using the standard BMI formula.

Things You'll Need

• Scales
• Measuring tape

Show More

Instructions

• 1

  Write down the formula to calculate BMI: weight in pounds / (height in inches^2) --- 703

• 2

  Weigh yourself. An accurate weight in pounds is essential to calculating BMI. Weigh yourself on your home scale, or use the number from your most recent medical checkup.

• 3

  Measure your height in inches. You may also use the number from your most recent checkup. Convert the number of your height in feet by multiplying it by 12, then add on the leftover inches. For example, a person who is 5 feet 8 inches tall would write down 68 inches (5 --- 12 + 8 = 68). Multiply this number by itself to obtain the number of inches squared. For example, 68 --- 68 = 4,624.

• 4

  Divide your weight in pounds by your height in inches squared (160/4,624 = 0.03). Multiply this total by 703 to get your BMI. For example, a person weighing 160 lbs. at 5 feet 8 inches tall would have a BMI of 24.

• 5

  Use a chart, such as the one featured on the CDC website, to determine if your BMI falls within a healthy range. If you are over or under the healthy BMI range, your doctor can recommend a course of action.