BMI Calculators: What is BMI - and How to Calculate Yours)

BMI Basics, including the BMI Formula and BMI Calculators as well as BMI information for children and teens

You know your body weight, but do you know your BMI?

Your BMI (or Body Mass Index) is a quick way to figure out of if your weight is on track for your height. 

Your BMI is very simple to calculate but keep in mind that it should be used only as a guideline for healthy weight. Because muscle weighs more than fat, weight and your BMI are not the only determination of your level of health.

BMI Calculator
Use the BMI Calculator here - or use the formula outlined below. 

Weight: lbs.
Height: Ft. In.

Body Mass Index
According to the Panel on Energy, Obesity, and Body Weight Standards published by American Journal of Clinical Nutrition, your category is:
Visit JustNutri.com for info on inproving your BMI

Your BMI falls within one of four categories: underweight, normal range, overweight or obese.

  • Underweight is 18.5 and below
  • Normal is 18.5 to 24.9
  • Overweight: 25.0 and 29.9
  • Obese: 30 and over 

The BMI Formula
In order to calculate your BMI just complete the following steps. All you'll need is yourself, your accurate height, a scale and a calculator.

1. First, weigh yourself. If you normally weigh yourself once during the day at a specific time you're going to do things a little bit differently this time. You need to weigh yourself in the morning before you eat or drink because food and liquids can affect your body weight. Weigh yourself three times and then take an average of those weights to get an accurate figure.
 
2. Next, convert your height into inches and then square that figure. For example, if you are 5'5" your height in inches would be 65 inches. Square that number (65X65) and then divide your weight in pounds by that figure. If you're 5 feet, 5 inches tall and weigh 165 pounds, your ending number would be .03905.
 
3. The next step is to take that number and multiply it by 703 (see why you need a calculator!) This step will convert the pounds and inches into the metric system. In our example, .03905 multiplied by 703 is 27.45. This figure is your BMI and, again, it falls within one of four categories: underweight, normal range, overweight or obese.

  • Underweight is 18.5 and below
  • Normal is 18.5 to 24.9
  • Overweight: 25.0 and 29.9
  • Obese: 30 and over 

BMI for Children

All adults over 20 years of age can use the BMI chart above.

BMI for children and teens is calculated the same way that it is for adults, but the results are not determined via a static chart (as above) but through a comparison with other children of the same age and sex.

  • If the BMI-for-age is less than the 5th percentile the child is underweight.
  • If the BMI-for-age is between the 85th and 95th percentile, the child is at risk for becoming overweight.
  • If the BMI-for-age is in the 95th percentile, the child is overweight.

Here's a great BMI calculator for children and teens that will determine both the BMI and the the child's BMI percentile: http://pediatrics.about.com/cs/usefultools/l/bl_bmi_calc.htm

Keep in mind that a BMI is only a screening tool that is used by doctors and healthcare professionals to categorize your weight. There may be other factors that contribute to your high or low number that have nothing to do with your weight, like a long-term illness that produces an underweight BMI or lots of muscle mass that produces a high BMI.
 
Once you determine your BMI, you should check with your doctor if you're outside of the normal range. Your doctor can provide you with solutions to help you either gain or lose weight when needed. You should not undergo any weight loss or weight gain program without first consulting your doctor, who can offer additional testing and nutritional counseling that can help you meet your goals.

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