How to Use a BMI Calculator

Even though calculating body mass index is fairly easy once the formula is known, a BMI calculator can make the job even easier. BMI calculators are simple to use, and can eliminate human error when determining the BMI number.

Instructions

Difficulty: Easy

1. Select the measurement system you wish to use. A BMI calculator is able to calculate body mass index either in United States measurements or metric measurements. The BMI calculator at the Mayo Clinic's website has a button that changes the measurement system (see Resources below).
2. Input your weight into the BMI calculator. The weight will either be measured in pounds or in kilograms, depending on the measurement system used. A BMI calculator such as the one at the Partnership for Healthy Living does accept decimal numbers for extra precision (see Resources below).
3. Enter your height into the BMI calculator. A BMI calculator using metric measurements will need to use the height as measured in meters, while a BMI calculator keyed to United States measurements will need the height as measured in inches.
4. Hit the enter or calculate button located on the BMI calculator and observe the results. If you have followed the steps correctly, the resulting number should be somewhere between 18 and 40. A number below or above that range means that you are extremely underweight or extremely overweight, respectively.
5. Double-check your results. Even though a BMI calculator won't make a mistake, the numbers for the height and weight may not have been input correctly or the BMI calculator may not have been keyed to accept height and weight in the desired units of measurement. Input the numbers again, and the BMI calculator will provide the same result if the numbers were right.
6. Check your BMI number against the chart that the calculator provides. Almost all BMI calculators, such as the one at the National Heart Lung and Blood Institute, contain some sort of chart or key to explain what the BMI number says about how fat or thin a person is (see Resources below). This will provide you with a good reference point in order to make diet plans, fitness plans or provide reassurance that you're keeping yourself healthy.

Tips & Warnings

• If your BMI number seems very inaccurate, such as a decimal number or above 50, make sure you are using the proper measuring unit. BMI calculators vary concerning whether they are initially keyed to accept metric measurements or United States measurements.