Measurement Tools — BMI

What It Is

BMI (Body Mass Index) is a relationship between weight and height that is associated with body fat and health risk.

Equipment Used

  • Scale measures weight.
  • Height is measured by a tape measure or preferably by a stadiometer, which is a special device on many scales used for measuring height. It is typically found in a doctor's office or clinic.

How It's Done

Weight is converted to kilograms, height is converted to meters and then squared. These numbers are then put into an equation to determine BMI: BMI = kg/m2.


  • It's easy to look up on a BMI chart.
  • Many studies have identified the health risks associated with a wide range of BMIs (both high and low values.)


  • It can misclassify up to one out of four people.
  • It does not take into account location of body fat.
  • It cannot accurately classify elderly individuals who are frail and sedentary.
  • It cannot accurately classify body builders.
  • It does not distinguish between body fat and lean body mass.

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