How to Calculate Body Fat Percentage From BMI

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Your body mass index, or BMI, indicates your fat ratio in relation to your frame or height, and a few quick calculations can show you whether your weight and height fall into a healthy BMI range. Do the math from the help of this free video on nutritional calculations.

Part of the Video Series: Nutritional Calculations
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Video Transcript

Hi, I'm Charlotte Lawson, a registered and licensed dietitian. Now, if you've gotten your BMI, you might be wondering, "How can I calculate my body fat percentage from my BMI reading?" Well, unfortunately, these two numbers don't necessarily coincide. The BMI is really a ratio, as far as how much your frame or height is carrying. Body fat percentage is really a multitude of combinations, as far as calculation-wise. There's no direct math equation that you can plug numbers into to find a body fat percentage, but there are different techniques. You can see a professional who has been trained to do the body fat skin fold caliber test, and they take a couple different measurements, and then plug those numbers into an equation, or you can do a bio-electrical impedience test that sends a little bit of an electrode through your body. The more lean muscle mass you have, typically, the better the electrode will conduct, and therefore gives a certain percentage, which then evaluates your body fat percent as well. You can also maybe spend some big money and get the water ratio or water displacement test, which really is the best form, and is what we consider the gold standard, if you will. Now, one calculation I can help you figure out, and that really is a good predictor of health risk, is your BMI or body mass index. Now, this is a range, again, of how much weight that your height is carrying, and really can help us to predict or categorize our risk for health or chronic diseases. The higher your BMI, typically the higher risk. And there is is a certain level as well, dropping below a level or reading, excuse me, a number of 18 also has been proven for decreased health. So, I'm going to show you an example here. This is kind of what I consider the cheater version, but not having to use or excuse me, convert the standard forms of height and weight to metric. So, I'm going to use my weight in pounds, and my height in inches. Now again, this is kind of an easy way to do it, but it gives a correct reading. So, I weigh 140 pounds. I'm going to multiply that by 703, divide that by my height, which is 64, and six squared, pretty much. This is exactly what I'm going to punch into my calculator. So, I have 140 times 703, equals a big 98,000 number, divide it by 64, divide it by 64 equals 24. My BMI equals 24. Now, a healthy range is anywhere between 18 and 25. Now, if you hit over 25, you're considered in the overweight range, and above 30 you're considered obese. Now again, any small change in BMI really significantly can improve your health risk. So say for instance, you were in the obese category and you're looking to lose weight. And your overall goal is just to at least get into the overweight range, or eventually into a healthy range. Even if you've gone from 30 to 29, your health risks or risk for health has significantly improved, and you're not nearly as as much risk as you were before. Now again, this is the equation for BMI, not body fat percentage. But check in with a trained professional if you're interested in that body fat percent ratio. I'm Charlotte, and eat happy.


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