How to Calculate BMI With a Formula

Overview

When it comes to the body, there are several assessments utilized as indicators to your general health. Some of these include scale weight, body fat percentage, lean muscle mass and BMI, or body mass index. Body mass index is a reading of the amount of fat you have in relationship to your height and weight. It can be determined by plugging information into a computer, or it can be done by the use of a formula. When you use the formula, there are a few easy steps that need to be done.

Step 1

Find out your weight. Step on to the scale on an empty stomach first thing in the morning after you used the bathroom. This is the best time to get your most accurate weight. To make it even more precise, wear no clothes or just wear underwear.

Step 2

Find out your height. Stand with your back to a wall or stand inside an open doorway. Use a pencil to place a mark on the wall at the top of your head. Use a tape measure to calculate your height in inches, then square this number.

Step 3

Use the formula. Divide your weight by your height, and then multiply by 703 to get your body mass index. Here's an example using a man who is 6-foot-2 and weighs 200 lbs.: 703 x (200/74 x 74) = a BMI of 25.68.

Step 4

Compare your results. There is a chart that you can cross reference your results to for checking your BMI range. If you are less than 18.5, you are considered underweight. If you are 18.5 to 24.9, you are considered normal. If you are 25 to 29.9, you are overweight, and if you are 30 or above, you are considered obese.

Step 5

Use the metric system. You can also use a metric system formula to calculate your body mass index. In this case, take your weight in kilograms and divide it by your height in meters squared. One kilogram equals 2.2 lbs., and 1 inch equals .0254 meters. Here's an example using a woman who is 5-foot-2 and weighs 120 lbs.: 120/2.2 equals 54.55 kg and 62 x .0254 = 1.57 meters. 54.55/1.57 x 1.57 = a BMI of 22.1.