Understanding Underweight: Signs, Risks & BMI Calculation

If you are underweight, you risk health problems. A woman's periods can stop, your bone density can decrease, and you can be nutritionally deficient. One way to determine whether you are underweight is to calculate your body mass index, or BMI, a measurement of an adult's body fat based on height and weight. For the most accurate BMI reading, have your doctor or gym trainer test it. For a rough idea, calculate it yourself using this simple equation.

Things You'll Need

• Pencil
• Paper
• Calculator
• Scale
• Tape measure

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Instructions

Calculating BMI

• 1

  Weigh yourself on your scale in pounds and note the result.

• 2

  Measure your height with your tape measure. Convert feet into inches by multiplying the number of feet by 12, and add on any remaining inches. For example, if you are 5 feet, 5 inches, multiply the 5 feet by 12, which equals 60, and add on the extra 5 inches, for a total of 65 inches.

• 3

  Square the number of inches--that is, multiply it by itself. For example, multiply 65 by 65, for a total of 4,225.

• 4

  Take your weight in pounds, and divide that number by your squared height. Using the same example, if you weigh 140 pounds, take 140 and divide it by 4,225. The result would be .03.

• 5

  Multiply the result (.03) by 703 since you are using pounds. (If you use the metric system--kilograms and meters--skip this step.} Using the same example, your result would be 23.29, which falls in the category of a normal BMI (18.5 to 25}. A result of 18.5 or below is considered underweight.