How to Calculate Your BMI (Body Mass Index)

Your body mass index (BMI) can be calculated in numerous ways. A fast and easy way to calculate your BMI is to use the calculator available from the National Heart, Lung and Blood Institute. Simply click here to use the calculator to determine your BMI. But keep in mind, this is just a generic figure that is given based on your height and weight.

Body Mass Index

If you want to perform this calculation manually, you can do so by following these 5 steps:

  1. Weigh yourself on your bathroom scale to determine your current weight (in pounds).
  2. Measure your height using a tape measure, noting both the feet and inches.
  3. You’ll want to convert your height into just inches and square it. For example, if you’re 5’11, you would perform the following equation (5*12) +11 to determine your total height in inches. Then, you would take this number and multiply it by itself.
  4. Divide your weight by the figure calculated in step three.
  5. Multiply the figure derived in step four by 703.

If you happened to used kilograms and meters to measure weight and height, skip step five.

Determining the Results

The final step of the calculation provides you with a number. This number reflects your BMI. In general, the following BMI scale exists:

  • A BMI that is under 18 indicates that you’re underweight.
  • A BMI that is less than 18.5 indicates that you’re thin.
  • A BMI between 18.6 and 24.9 indicates a healthy weight.
  • A BMI between 25 and 29.9 means that you’re overweight.
  • Any number higher than 29.9 indicates that you’re in the obese range.

Body mass index isn’t a very valid number because it doesn’t indicate how much fat a person has on their body. For example, a bodybuilder may be 240 pounds of muscle while only being 6 feet tall. For a normal person, this weight would put them in the obese range. But bodybuilders may have a low level of fat on their body, so they’re technically not obese.

Many scales will have a body fat calculation that allows you to determine the approximate amount of body fat you have, but scales are not always accurate.

Instead, you’ll want to use another method to determine how much body fat you have. There are several ways to measure body fat, and the best ways are:

  • DEXA Scans: These scans utilize x-ray technology to determine the amount of lean tissue, fat, bone and minerals in the body. These scans also determine where your body holds most of its weight, but you’ll need to get a physician to undergo the scan.
  • Underwater Weighing: This method requires that you weigh yourself underwater. Muscle is far denser than fat, so you’ll be to determine your body density by weighing yourself in the water. But you must be fully submerged for proper calculation.
  • Caliper Method: The caliper method uses skinfolds to determine body fat percentage. Between three and seven sites are needed to determine the fat level in the body. This is a very popular method, and one that can be done by yourself (if you know the proper skinfold locations), or by trainer or doctor.

The amount a person weighs is often far less important than their body fat levels. If you’re looking to tone up, you may stay the same exact weight that you are now, but lose fat to make you look more muscular and fit.