How to Calculate BMI Z Score

Body mass index, or BMI, is a measurement of body fat determined by a simple calculation using height and weight. The Z score, the number resulting from the calculation, indicates where you fall in the range of body fat measurements. For people ages 20 and older, a Z score below 18.5 means you are underweight, 18.5 to 24.9 means you fall in the normal range, 25.0 to 29.9 means you are overweight and a score of 30.0 and higher means you are obese.

Things You'll Need

• Calculator
• Your height and weight measurements

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Instructions

How to Calculate BMI Z Score

• 1

  Decide whether you will be using pounds and inches or kilograms and meters to determine your BMI.

• 2

  Convert your height from centimeters to meters for the metric calculation or from feet to inches for standard calculation. For example, a height of 152 centimeters, which is approximately 5 feet, becomes 1.52 meters or 60 inches.

• 3

  Divide your weight by your height squared. If you are using metric measurements, divide your weight in kilograms by your height in meters squared. For example: 45 kg / (1.52 m)² = 19.5. If you are using pounds and inches, divide your weight in pounds by your height in inches squared, and then multiply by 703. For example: 100 lbs/ (60 in)² x 703 = 19.5. Both calculations result in a BMI of 19.5, which is in the normal range.