Body mass index is a measure that uses a person's height and weight to create an overall numeric value. Body mass index assesses whether a weight is appropriate for a corresponding height. The majority of BMI scores fall into a general range of 15 to 35. After inserting the variables and running the calculation, the resulting value will fall under one of four possible outcomes: underweight, normal weight, overweight, and obese.

The only two variables needed to calculate body mass index are weight and height. BMI was originally designed using the metric system, but the American system of measurements uses pounds for weight and inches for height, so these are the units that will be used in this body mass index calculation. If you are working with metric units, the equation is more simplistic: (weight in kilograms) / (height in meters squared).

Using the weight and height values, plug them into the following equation: (weight in pounds x 703) / (height in inches squared). Round the result to the nearest whole number or to one decimal. For example, a person with a height of 5 feet 7 inches (67 inches) and a weight of 160 pounds has a body mass index of 25 from the equation (160 x 703) / (67^2).

A person with a BMI value below 18.5 is considered underweight. The lower the underweight value is, the more extreme the case. BMI scores above 18.5 and below 25 are considered ideal, normal body mass index scores. A BMI between 25 and 30 generally means a person is overweight. A BMI above 30 is considered obese. Considering variations in body type, these values are not necessarily static.

The interpretation of these values is not set in stone. For instance, a person with a BMI over 30 is not necessarily obese; this is because BMI does not consider the proportion of muscle mass to fat mass in the equation. The result is that when examining the BMI of the average athlete, they are frequently classified as overweight or obese due to their builds, when this is clearly not the case. Basically, BMI has its uses, but it is a simplistic and dispassionate measure that may or may not be valuable on a case-by-case basis.

When measuring a person's ideal weight, body mass index is a good starting point, but it cannot necessarily draw a fully accurate conclusion. People with a high level of muscle mass are unjustly penalized by BMI, making an analysis of body fat composition a more reliable measure.

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