How to Calculate BMI for Teenagers

Body Mass Index (BMI) is a statistical measurement that compares height, body weight and age to determine if a person is over or underweight. A teenager's BMI is compared to the measurements of a standard population of the same age and gender to determine a percentile score. BMI should be used in conjunction with other factors to determine a teenager's ideal body weight.

Instructions

1

Take measurements in metric units if possible. Measure the teenager's height in meters with a metric measuring tape. If you're measuring the height in centimeters, divide by 100 to determine height in meters. Weigh the teenager in kilograms.

2

Calculate the BMI for metric measurements. To determine BMI, divide the weight by height squared: (w/h^2), where w is the teenager's weight in kilograms and h is the teenager's height in meters.

3

Convert English units of measure to metric units if necessary. If you measured the teenager's weight in pounds and height in inches, you'll need to multiply h/w^2 by 703 to calculate the teen's BMI.

4

Record the BMI value to one decimal place and refer to the correct BMI chart for the teenager's gender. Locate the teenager's age to the nearest fourth of a year on the horizontal axis. Follow that hash mark vertically up the chart until you cross the teenager's BMI on the vertical axis.

5

Record this point on the chart and compare its vertical position with respect to the BMI percentile curves on the chart. This should provide an estimate of the teenager's BMI percentile to the nearest 5 percent. A BMI percentile below 5 percent is considered underweight, a BMI percentile in the range of 85 to 95 is considered overweight and a percentile greater than 95 is considered obese.