Body mass index (BMI) is a method of comparing your height to your weight. Doctors commonly use the BMI to identify patients who may be underweight or overweight. The raw BMI score isn't particularly useful for evaluating a child's weight because they're still growing. This will require you to convert a child's raw BMI score into a BMI percentile. This allows you to compare a child's BMI to those of other children with the same age and gender.
Step 1
Weigh yourself in pounds with a bathroom scale. This example assumes that your weight is 142 lbs.
Step 2
Measure your height in inches with a tape measure. This example assumes that your height is 66 inches.
Step 3
Compute your BMI. This calculation uses the equation [w / (h x h)] where w is your weight and h is your height.
This example assumes that your weight is 142 lb. and your height is 66 inches. Your BMI is therefore [142 / (66 x 66)] = 0.0326 pounds per square inch (lb/in^2.)
Step 4
Convert your BMI from units of lb/in^2 to units of kilograms per square meter (kg/m^2.) This requires you to multiply your BMI in lb/in^2 by 703 to obtain your BMI in kg/m^2.
This example assumes your BMI is 0.0326 lb/in^2. Your BMI is therefore 0.0326 x 703 = 22.9 kg/m^2.
Step 5
Determine your BMI percentile. Select the boy's or girl's BMI chart according to your gender. Locate your BMI on the vertical line of the chart and draw an imaginary horizontal line on that point. Locate your age on the horizontal line of the chart and draw an imaginary vertical line on that point. Locate the point on the chart where these imaginary lines intersect. Compare this intersection point to the BMI percentile curves on the chart to estimate your BMI percentile.
This example assumes you're a boy. You have a BMI of 22.9 and you're 17 years old. Your BMI percentile is about 69.
Things You'll Need
- Bathroom scale
- Tape measure
- Calculator
- BMI chart
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