How to Calculate BMI for Girls

A child's height and weight change rapidly between the ages of 2 and 19, so many factors--from lifestyle to hormones--affect this balance. One way to make sure a child is in good health is to calculate his or her Body Mass Index (BMI). This ratio of height to weight allows parents and doctors to gauge whether or not the child is the ideal weight for his or her height and activity level. However, this process is calculated a bit differently for girls than it is for boys. Here is how to properly calculate a girl's BMI for a more accurate picture of her overall health.

Things You'll Need

• Calculator
• Tape measure for height
• Accurate weight scale
• Pen and paper

Show More

Instructions

Calculating BMI for girls

• 1

  Measure the child's height and weight. With the child standing against a flat surface such as a wall and standing on a flat floor with no carpeting, use a standard tape measure to measure from the floor to the top of the child's head while she is standing straight, wearing no shoes or hair accessories. Weigh the child using as accurate a scale as possible--preferably a digital scale--while she is wearing minimal clothing and no shoes.

• 2

  Calculate BMI using a standard formula once an accurate height and weight are obtained. First, square the height measurement in inches. For example, if the child is 36 inches in height, multiply 36 by 36. Then, divide the child's weight by the squared height number. Then, multiply the result by 703. So, the formula would be read like this: weight / height squared x 703.

• 3

  Use a BMI growth chart to plot your child's BMI according to her age. The growth chart will determine what percentile the child's BMI falls into for her age. The percentile range for healthy weight and BMI is from 5 percent to 85 percent, with less than 5 percent being underweight and more than 85 percent being overweight. A child whose BMI falls into the 95th percentile or greater for her age is considered obese.