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Health 

What Is Body Fat and How Do You Measure It?

June 17, 2020 8 min read

What Is Body Fat and How Do You Measure It?

Dr. Amanda Anderson, PT, DPT, MS. - Contributing Writer, Physician’s Choice

The dreaded word: FAT. Is it really as bad as everyone makes it seem?

Your body fat percentage is defined as the amount of fat in your body compared to your other tissues, including organs, muscles, bones, tendons and water weight. We need a healthy body fat percentage for optimal health benefits, but as with anything, too much of a good thing can also be a problem.

Why is body fat percentage important?

In order to survive, a percentage of your body must be composed of fat. Fat protects your internal organs and allows you to store energy. Everyone has a level of fat they must maintain for survival, which is called your essential fat limit. Women typically have a higher body weight percentage than men because of their differing reproductive needs. Men also just naturally have more lean body mass.

The American Council of Exercise (ACE) recommends the following body weight percentages for men and women, broken up into various categories (1):

How does body fat impact your weight?

Body fat is a component of your overall weight. Remember, when you get weighed, it’s not only including your body fat that is being weighed, but also your bones, organs and other tissues.

It is important to note that your body fat percentage does not take into account how much lean muscle mass you have. Two people with similar body fat percentages can look vastly different from each other, especially if you’re looking at differences between men and women.

For example, a male athlete may be five percent body fat, while a woman who looks comparable in terms of her athleticism and shape may be 12 percent body fat.

Body fat percentage versus body mass index (BMI)?

Body mass index (BMI) is not the same thing as body fat percentage. First, it doesn’t take into account your gender, ethnicity, or age, all of which are important factors in body fat distribution. BMI is based solely on your height and weight. It does not measure body fat directly but has been correlated with more direct measures of body fat percentages, which will be discussed below.

BMI is used as a cost-effective screening tool for weight and can be helpful in determining if a person requires additional testing or resources for weight management.

According to the Centers for Disease Control and Prevention (CDC), BMI for adults over the age of 20 is interpreted according to the categories listed in the table below (2).



The CDC also has a BMI calculator for children between the ages of 2 and 19 (3).

BMI is calculated by taking a person’s weight (in kilograms) and dividing it by the square of their height in meters. There are many body fat calculators available online for determining your BMI (4).

Keep in mind that even if two people have the same BMI, their levels of “body fatness” may be vastly different. Again, BMI is an excellent screening tool, but for more accurate measures, body fat percentage testing should be completed.

So how do we measure body fat percentage?

This is really the big money question. Why do you keep stepping on the scale only to see no results? You’ve been exercising daily, keeping track of your diet, drinking enough water, and getting enough sleep. Aren’t those the ingredients for success?

Sometimes, knowing your body weight percentage, or what your actual weight is made of, can be helpful. It will allow you to better tailor your weight loss program to focus more on fat burn.

There are many different ways to measure your body fat percentage.

How to measure your body fat percentage at home

1. Skinfold calipers

The skinfold measurement technique is probably the most common assessment technique utilized by consumers, personal trainers and other health professionals, in order to determine body fat percentage. This technique is inexpensive and yields relatively accurate results, with a 3.5 percent margin of error. The key to skinfold caliper measurements is ensuring that the person doing the testing is experienced with the technique and the same person is doing the testing each time. If not, the accuracy of the body fat percentage measurements decreases significantly.

You can take a look at some examples of skinfold calipers available for purchase on Amazon and other sites. They range in price from $3 to $300.

The procedure for skinfold caliper measurements is based on specific anatomical locations that are different for men and women, since they store fat differently.

For men, the skinfold sites are at the chest, thigh, and abdomen. For women, the skinfold sites are at the triceps, thigh, and suprailium. There are also methods in which seven sites are measured instead of three. If you purchase a pair of skinfold calipers, the directions included will direct you through the proper technique and what anatomical sites you need to measure (6).

2. Body circumference measures

Your specific body type provides important information about how and where your body fat is distributed. Measuring the circumference of certain body parts is a simple way to estimate your body fat percentage.

The U.S. Navy uses a body fat calculator that takes a person’s age, height, and some circumference measurements using a standard tape measure (7). For men, the neck and waist circumference are plugged into the calculator. For women, an additional hip measurement is added in addition to the neck and waist measurements.

While the accuracy rate of this technique can depend on measuring abilities, it may still give you a good idea of what you need to work on and where you need to focus.

Other ways to measure your body fat composition

The measurements below may not be as readily available and tend to be more expensive; however, they do tend to be more accurate and not as dependent on the experience of the measurer.

1. Dual-energy X-ray absorption (DEXA)

You may be more familiar with a DEXA scan as a method of assessing bone density, but it can also be used to gather information about lean mass and where you tend to store fat.

You typically lay on your back for about 10 minutes while you are scanned by the machine. The amount of radiation that you receive from a DEXA scan is negligible. While this method of determining body fat percentage is reliable (2.5 - 3.5 percent margin of error), this method is usually widely unavailable to the general population and is generally only seen in medical or research settings (6).

However, if you’re interested in finding out if DEXA is an option in your area, check out the DexaFit website (8).

2. Hydrostatic weighing

Also known as underwater weighing or hydrodensitometry, hydrostatic weighing weighs you while you are underwater after you have exhaled as much as you can. This is compared to the amount you weigh on land. This information is then plugged into various equations in order to best estimate your body fat percentage.

When testing is performed correctly, it is very accurate and can yield as low as a two percent margin of error (6). While many hydrostatic testing devices are only available in medical and research facilities, check out DexaFit for the availability of hydrostatic testing in your area. Similarly, some large urban areas have mobile hydrostatic testing available, so a unit can come to your gym or facility for testing of your members.

3. Air displacement plethysmography (Bod Pod)

Like hydrostatic weighing, air displacement plethysmography (ADP) estimates your body fat percentage based on air instead of water.

For the test, you sit in a small chamber shaped like an egg for several minutes while the pressure inside the space is varied. The relationship between the amount of space you take up in the chamber and the pressure of the air in the pod is how your body density is measured and your body fat predicted.

Typically, Bod Pods are unfortunately only available at universities or research institutions. They have a low error rate, between two and four percent (6).

4. Bioelectrical impedance analysis (BIA)

With bioelectrical impedance analysis (BIA), electrodes are placed on your skin and electrical currents are sent through your body tissues. The equations derived from these tests are based on the fact that electric currents move through muscle faster than through fat because of the higher water content of your muscles. Because of this, your results can be skewed by your food and/or fluid intake prior to testing.

BIA devices vary widely in terms of price, but can be purchased by consumers. Unfortunately, the more inexpensive units tend to be less accurate (6).

How do you pick which way to measure your body fat?

The method you choose to measure your body fat really depends. None of the tests are foolproof and the “gold standard” test would include information from all of the tests combined. However, this may not be cost-effective or feasible for most people.

Really ask yourself why you want to know your body fat percentage. Do you need the numbers from your testing to be as accurate as possible? Or, does a little inaccuracy not matter since you’re going to be re-measuring yourself frequently to see how you’ve improved? Can you afford to have your testing done somewhere, or do you want a method that you can do and repeat at home?

While skinfold measurements and using a tape measure may seem archaic and not as accurate, they may be the best choice for you. If you aren’t planning on getting yourself tested as often and can afford a DEXA, hydrostatic weighing or ADP session, these may be better options if your ultimate goal is accuracy.

Whatever method you decide to pursue, it is important that you repeat the same method in order to see results. There will not be carryover in progress between the different types of measurements.

Typically, any results, wherever they are completed, will be more accurate in the morning on an empty stomach after you’ve emptied your bladder and/or bowels. You should also complete your BIA testing before you have had anything to drink.

So why is knowing your body fat percentage important again?

Knowing your body fat percentage is definitely not a must. However, having some idea about where you store fat and your body shape, even if you just use your BMI, is a good idea. A person’s level of body fat is directly linked to many health outcomes. Obesity causes heart disease, type 2 diabetes, high blood pressure and stroke. Even just having a general idea of your BMI can be motivating to help you live a healthier lifestyle and stick with a weight loss program.

In summary

It is important to take all body weight percentage measurements with a grain of salt. None of the tests are foolproof. You need to make sure you are using your body composition percentages as a piece of a bigger health puzzle. Starting a weight loss program or trying to reduce your body fat doesn’t mean you should neglect how you feel day-to-day. Keep track of how your clothes are fitting, your mood during the day, how tired you feel, how hungry you are and how you feel during your workouts. You are not your body weight percentage. If you don’t listen to what your body is telling you on an everyday basis, you will not see your body fat percentage numbers drop.