How Do I Calculate My BMI (Body Mass Index)?
Posted August 4, 2008 by Mister Knowitall

I’ve been told that knowing my BMI or Body Mass Index is important to my health. How do I calculate it?

The formula for your BMI is relatively simple so long as you know your height in meters and your weight in kilograms. If you don’t, the conversions are pretty simple so long as you have a calculator.

Your weight in kilograms is your weight in pounds divided by 2.2. Your height in meters is your height in inches times 2.54, and then divided by 100.

Now that you have the two numbers, multiply your height in meters by itself to get its square, then divide your weight in kilograms by that number. The resulting number is your BMI. Or, if you find that a bit too difficult, here’s a simple calculator. You can enter your weight in pounds or kilograms and your weight in inches or centimeters. This uses the free BMI calculator script at Calculators-Free.com.

Calculate Your BMI

About the Results

Calculating your BMI is easy. Interpreting the numbers is a bit harder. While there’s a standard set of ranges for underweight, normal weight, etc., these are better taken as general guidelines than as gospel. They’re based on sets of averages and norms that are not one-size-fits-all.

One of the prime examples of how BMI is not universally appropriate is when it’s applied to bodybuilders. The BMI makes no distinction between muscle and fat. It’s just a straight calculation based on simple numbers. So a shorter man who has packed on a lot of muscle can end up with a very low bodyfat percentage, yet still have a BMI calculator tell him he’s obese.

Recently, BMI had an extra calculation added to it, but only if you’re from China or Southeast Asia. Apparently, the calculation needs a bit of adjustment to help those folks to better fit the definitions of underweight, normal weight, etc. And it’s possible more calculations based on other factors will be added gradually so that BMI gets more accurate.

Under no circumstances should you take what an online BMI calculator says as gospel or as some sort of health advice. Your BMI is merely a starting point for a conversation with your doctor or other health professional.