How To Calculate Body Fat Percentage

Calculating body fat is still an imperfect science. There is no direct way to measure body fat percentage. Every body fat calculating test has a margin of error, some more than others. This article goes over ways to measure body fat and the accessibility of each way to calculate body fat. 


How To Calculate Body Fat Percentage 

There is no direct way to measure body fat. There are only ways to measure other things that will give us insight into predicting our body fat within a certain margin of error.


BMI (Body Mass Index) 

The basis for BMI was created in the 1800s and was not used until the 1970s to measure obesity. Since then, it has been the single most well known way to measure body fat and it is completely inaccurate. In fact, the creator of the BMI chart explicitly said it shouldn’t be used to measure body fat.


Why BMI Is The Worst To Use To Calculate Body Fat Percentage 

The BMI is so widely used in part because it is so accessible. All you need to know is someone’s height and weight, however solely relying on those two basic measurements makes it in no way even close to accurate. Muscle weighs more than fat, so there’s no way to account for extra muscle mass. Not to mention, bone density is also not accounted for. So, two people with entirely different body compositions will score the same on the BMI scale. The BMI system has little actual value and is best to never be used. 


Bioelectrical Impedance Devices 

Bioelectrical impedance devices measure body fat as well as lean mass by assessing the impedance or resistance to a small electric current passed across body tissues, or so it claims. You usually see these devices at the gym or installed in home scales. Bioelectrical impedance devices are portable, non invasive, and cost effective, which is why they are popular to use. 


Why Bioelectrical Devices Aren’t The Best

A study in 2003 showed Bioelectrical impedance devices found a “tendency to overestimate body fat in lean subjects and underestimate body fat in obese individuals”. Their margin of error can be upwards to 8%, which is incredibly high. The reasons for such poor measuring is due to variations found with not only hydration but also sensor placement, glycogen levels, and variations in equations by manufacturers.



The skinfolds test (“pinch an inch”) is actually the most accurate accessible test, with a margin of error between 4-7%, which is still high and based on the expertise of the individual giving the test. Although the skinfolds test has a big margin of error, it can be a good way to measure body composition trends over time. 


How To Assess Skinfolds 

You’ll need a skinfolds measuring device and there are youtube videos that go over the technique. The tester usually tests 3 sites on the body: the chest, abdomen, and thigh on men and triceps, suprailiac, and thigh on women. There are specific measurements to be taken to find the exact testing site. The participant must relax the muscle group that is being assessed. When skin fold is pinched, the practitioner should be taking their reading at the middle of the pinched skin, not apex or base. Retake each site in order to obtain accurate readings.


The Bod Pod 

The Bod Pod is an egg-shaped device that you sit in to measure your weight and volume to determine your body density and calculate your percentage of body fat. It’s a very expensive piece of equipment and is really only available in academic settings or medical centers. If you live in a large city, you might be able to get your body fat tested by the Bod Pod for a small amount of money. 


Why The Bod Pod Is More Accurate At Calculating Body Fat Percentage 

The Bod Pod uses air displacement plethysmography to calculate body volume, combined with highly accurate scales to measure mass (Kg) and uses this to calculate body density. A mathematical formula is then used to estimate fat percentage. The margin of error is 2-3%. 


Dexa Scan 

A DEXA scan is utilized to measure bone density and body fat with a margin of error between 2.5-3.5%. DEXA assesses body composition from reflected X-ray particles. A Dexa scan is more accessible than a Bod Pod, and will cost around $100 to get.


The Bod Pod Vs Dexa Scan 

Although the Bod Pod method is less expensive and is less invasive to subjects, DEXA is usually easier to access. The error of measurement with a DEXA scan can be even higher, and hydration and who is running the scan can impact results. 


Hydrostatic Weighing 

Hydrostatic Weighing is the gold standard for measuring body fat, with a 1-2% margin of error, and requires the subject to be completely submerged underwater. This testing works with the principle that states that the amount of liquid a submerged object displaces is equivalent to the volume of the object. By measuring your weight on land and your weight underwater, test administrators can calculate your body’s density. This test is relatively inaccessible, if you live in a city, hydrostatic weighing might be available to you. 


How To Test With The Hydrostatic Weighing System 

The test administrator measures and records your body weight on land. You then enter a water tank that has an underwater seat hanging from a scale. You submerge underwater while sitting on the chair and you have to breathe out fully.


Progress Pictures

Progress pictures are 100% accessible, underrated, and pretty accurate. Although it might be hard to calculate body fat exactly, you’ll be able to see body fat loss or gains through pictures over time. Have your coach or someone else look for the most accurate reading. For the most accuracy, take your pictures in the same room, same time of day, same day of week, with the same lighting. 


Final Thoughts On How To Calculate Body Fat Percentage 

There is no way to directly measure your body fat, unless you are going to cut it out of your body and place it on a scale. That’s why pivoting to other ways to measure your fitness levels like eating enough protein, seeing your strength gains, and body composition changes, are healthier ways of tracking progress and overall health than tracking your body fat. 


want to learn more? Listen to The Stronger Than Your Boyfriend Podcast, Episode 142: How to Calculate Body Fat Percentage: Why Current Fitness Measurement Tools Suck


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