How to Tell Calculate BMI for Teens

Overview

When it comes to the body, there are various assessments that are utilized to evaluate the status of your health. Some examples are body weight, body fat percentage, lean body mass and BMI, or body mass index. The body mass index is the amount of body fat you have in regards to your height and weight. When it comes to calculating BMI, it is done the same way for teens as it is for adults--there are a few numbers that get plugged into an equation.

Step 1

Weigh yourself. Weigh yourself first thing in the morning on an empty stomach right after getting out of bed and after using the bathroom, wearing as little clothes as possible. This will give the most accurate reading.

Step 2

Measure height. Stand with back against a wall or stand inside an open doorway. Take a pencil and place a tick mark on the wall at the top of the head. Using a tape measure, find your height in inches, then square it.

Step 3

Use the equation. The equation for BMI is 703 multiplied by weight, divided by height in inches squared. Here's an example using a teenage boy who is 5-foot-10 and weighs 160 pounds: (703 x 160) / (70 x 70) = a BMI of 22.96.

Step 4

Use the metric system. There is also an equation that uses the metric system. In this formula, take weight in kilograms and divide it by height in meters squared. To convert pounds to kilograms, divide by weight by 2.2, and to convert inches to meters multiply height by .0254, as this is the amount of meters in an inch. Here's an example using a teenage girl who is 5-foot-4 and weighs 130 pounds.
130/2.2 = 59kg
64 x .0254 = 1.63m
59 / (1.63 x 1.63) = a BMI of 22.18.

Step 5

Use an online resource. There are BMI calculators online where you plug the data into a search engine and BMI comes up in seconds. The Centers for Disease Control have one of these (see References).

Step 6

Interpret your results. If your BMI is under 18.5, you are considered underweight. If it is 18.5 to 24.9, you are considered in the normal range, 25 to 29.9 is overweight and 30 or above is obese (see References for BMI chart).