Body mass index (BMI) is a ratio of weight to height and is used as a quick guide to determine potential weight problems in children and adults. While a BMI below 18.5 or above 24.9 may indicate increased risk, only a health care professional can diagnose if a body weight above or below normal values indicates an actual health issue. According to the Centers for Disease Control and Prevention, the standard weight status categories for an adult BMI are: Below 18.5 is considered underweight; 18.5 to 24.9 is within the normal range; 25.0 to 29.9 is considered overweight; and a BMI above 30 is considered obese. The BMI ranges are the same for both men and women. You can use a spreadsheet to calculate and track your BMI.
Calculating BMI
Step 1
Confirm that your bathroom scale is accurate. If you need to reset or calibrate the scale, do so by following the manufacturer's directions.
Step 2
Stand on the scale and write your body weight down. Retake your weight by stepping off the scale and then back on again. If there is no difference between the two measurements, use this number for your BMI calculation. If the two measurements are not the same, weigh yourself a third time and use the average of the three measurements as your weight.
Step 3
Stand with your back against a wall, without shoes. Your heels, hips, shoulders and head should all be touching the wall. Have a friend mark your height on the wall with a pencil. Step away from the wall and measure the distance from the floor to that mark in inches. Write down this number and measure your height again using the same procedure. If there is no difference between the two measurements, use this number for your BMI calculation. If the two measurements are not the same, measure your height a third time and use the average of the three measurements as your height.
Step 4
Divide your weight by the square of your height and multiplying by 703. For example, to determine the BMI of a 180 lb. female standing 5 feet, 4 inches tall we would make the following calculations:
BMI = (weight in pounds / (height in inches x height in inches)) x 703
BMI = (180 / (64 x 64)) x 703
BMI = (180 / 4096) x 703
BMI = (0.04394) x 703
BMI = 30.89
Step 5
Open a new spreadsheet in a spreadsheet program. Enter the date and time of your measurements into the first cell, your weight into the second cell and your height into the third cell. Use the forth cell of your spreadsheet to track BMI, either by manually entering your data or by having your spreadsheet program automatically calculate your BMI for you based on the above formula. Consult your software's manual for directions on how to set up and run formulas.
Tips and Warnings
- BMI is age- and sex-specific for children and teens, and requires the use of a modified formula to take into account the amount of body fat boys and girls should have at various ages. The metric version of the BMI formula is: weight in kilograms / (height in meters x height in meters)
- Body composition is not taken into account when calculating BMI. This means your BMI may not accurately reflect your actual health or fitness level. BMI should be used only as part of a more comprehensive evaluation of health and wellness.
Things You'll Need
- Measuring tape
- Bathroom scale
- Spreadsheet software (optional)
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