How to Compute Body Mass

Body Mass Index (BMI) is a number based on an individual person's height and weight. It's an indicator of the amount of body fat on a person. Medical professionals use BMI to screen for weight and possible health issues. Although the BMI is not always representative of a person's fitness or overall health, it can be used to determine whether the average person is overweight or obese. Online BMI calculators are widely available, but it's easy to compute your BMI yourself as well. You can use one of two formulas, depending on whether you are on the standard or metric system.

Instructions

How to Compute Body Mass Index

1

Step onto the scale to weigh yourself. Record your weight, in pounds, rounding to the nearest tenth for digital scales.

2

Stand with your back to the wall and mark your height with a pencil. For the most accurate results, have a friend mark your height. Use the tape measure to measure your height, and record it in inches.

3

Compute your body mass index from these numbers using a calculator or by hand. If you have measured yourself in pounds and inches, use the following formula:

Your weight (lbs) / your height (in.) squared, multiplied by 703. The resulting number is your BMI.

The formula for someone with a weight of 160 pounds and a height of 5-foot-6, or 66 inches, would be (160 / (66 x 66)) x 703. They would have a BMI of 25.8, putting them just into the overweight category.

4

Compute your BMI using the formula for the metric system if you have measured yourself in meters or centimeters and kilograms. This formula is:

Your weight (kg) / your height (m) squared. You do not need to multiply by 703 if you are using metric measurements.

According to this formula, an individual with a weight of 50 kg and a height of 1.5 meters would have a BMI of 22.2, placing them within a healthy weight range.

Interpreting Your Results

5

Compare your BMI with a BMI table showing standard weight categories for different ranges of BMI. These charts are widely available from print and online health resources, but the standard categories are as follows:

A BMI of 18.5 or lower is considered underweight.

A BMI between 18.5 and 24.9 is considered a normal, healthy weight.

A BMI between 25.0 and 29.9 is considered overweight.

A BMI of 30.0 or higher is considered obese.

6

Evaluate your BMI with an assessment of your body composition and physical activity. Athletes and bodybuilders may have high BMIs due to the amount of muscle mass on their bodies, which means they often fall into categories typically considered overweight or obese. Some athletes may also have underweight BMIs due to their atypically low percentage of body fat. BMIs for older people and those who have lost muscle mass may also have BMIs that underestimate their body fat percentages.

7

Use a BMI chart to further interpret your results, if you wish. Charts show the BMI for various heights and weights and are often color-coded to show the range of underweight, healthy weight, overweight and obese BMIs. The chart may assist in comparing your BMI to those for your ideal weight category and determining how to raise or lower your BMI as necessary.