Your body fat percentage is a better indication of being in a healthy weight range than the BMI which was really intended for populations and not individuals and does not take into account someone’s muscularity.

So, how do you estimate your body fat percentage? In short, all methods, short of an autopsy, have inaccuracies. Some more than others, and getting a reasonable accurate estimate will usually come down to using a couple of different methods, including eyeballing it.

First, some definitions and explanations of terms for you:

Fat Free Mass (or Lean Body Mass – LBM): this is everything that is not fat and includes your organs, muscle, bone, food in your stomach and intestines and water. This is a very important point. LBM is not only muscle and this confusion has a lot to do with why people think they made hyooge muscle gains on a deficit. When you start exercising, and especially lifting, you can store about 4lb of glycogen and water in your muscles, sometimes more. So, all other things being equal, someone who starts lifting can see an increase of 4lb or so on the scale and a lot of folks say “you gained muscle”. No you did not, you gained glycogen and water. You did however increase your LBM.

Body fat (BF) is split into two different types: visceral fat, which is the fat surrounding our organs and subcutaneous fat, which is the more visible fat which is under the skin.

Body Fat Percentage (BF%) is simply your body fat divided by your weight.

The accuracy of the methods is tested against the ‘gold standard’ for body fat testing, which is a 4 compartment model where the body is divided into 4 components: mineral, water, fat, and protein. It involves measuring body density with underwater weighing or the Bod Pod, total body water using a technique called deuterium dilution, and bone mineral content using DEXA. Equations are then used to get the estimates for the four components. A four compartment model is very expensive and is only used in research studies. While the results are still an estimate, it is by far the best estimate that can be made on a live person and is the standard against which all other techniques are judged. To be clear, when someone has a DEXA scan, they are not having their BF% tested at this level of accuracy as all of these tests are not performed.



The following is a summary of different methods of estimating body fat. One of the best series of articles in my opinion on this is by James Krieger and I have unashamedly plagiarized his articles below.

DEXA (Dual-energy x-ray absorptiometry method)

This is a three compartmental model as it estimates fat, bone and everything else. It was once used for determining bone density and has now evolved into a technique for also estimating body composition.

It is a convenient and quick and unlike two compartment models such as hydrostatic tests and bod pods, DEXA is not subject to errors caused by variations in bone density (see later). However, there are sources of error, including inconsistent results between different machines and different software. The main source of error however is a similar one you will see in this post: hydration levels. In fact, is has similar and sometimes worse error rates compared to hydrostatic testing.

http://weightology.net/weightologyweekly/?page_id=260

Hydrostatic or Underwater Weighing

This is a two compartmental estimation (it estimates fat and fat free mass) where you are weighed in an underwater tank, while having the amount of water you displace also weighed. Fat-free mass is more dense than fat. These principles are used to calculate your body density. From this number, your fat and fat-free mass is estimated.

A lot of things can contribute to error in the measurement, such as not successfully blowing out all the air in your lungs plus the amount of air that is still present in your digestive tract and lungs has to be estimated.

However, the biggest source of error is where the body density is estimated and then converted into a body fat percentage. A formula is used to calculate body density but, as in many situations, the formula itself is a predictor that is based on a sample population, under which the person being tested may not fall, as well as the formula itself using other inaccurate body fat testing methods to establish a base. In addition, inaccuracies can arise due to hydration levels.

http://weightology.net/weightologyweekly/?page_id=162

Bod Pod (air displacement plethysmography)

The Bod Pod is a two compartmental method and is a computerized, egg-shaped chamber which is based on similar principles to underwater weighing. As such, you would think it would have similar error rates. Not true unfortunately. In addition to the errors that an arise from the hydrostatic testing, additional errors can be caused by, for example, body/facial hair, body temperature, moisture and the tightness of the clothing worn .The individual error rate for the Bod Pod can be very high. Hydrostatic weighing, despite some of its problems, is much more reliable.

http://weightology.net/weightologyweekly/?page_id=175

Bioelectrical Impedance (BIA)

These are the scales that you stand on or hold, such as the Omron or Tanita Scales. They involve running a light electrical current through your body.

The main issue with these devices is that hydration levels can significantly impact the readings. Also, there are inaccuracies due to the distribution of body fat as the current only runs through part of your body (in the case of scales, the bottom half and in the case of handhelds, the top half). The other main issue is that they use data gathered from other testing methods, which have their own accuracy issues (see above) and apply those variables to predict your BF%.

The error rates seen are as high as 8% and this method is not even a very good long term tool as where you lose your weight from and hydration levels can vary.

http://weightology.net/weightologyweekly/?page_id=218


Caliper/Skinfold Method

This is a very cheap method to use. Calipers can be obtained for as little as $5. Using the caliper you pinch the skin and subcutaneous fat at a number of places on your body and measure the thickness of the skinfold with the caliper. A formula is applied to these numbers which will give you your body density which in turn is then converted into a body fat percentage using another equation.

There are a lot of errors that can occur with this method, the main one being user error by using the wrong technique to pinch the skin and fat. Also, someone's body fat distribution can impact the result. Another problem is with the formulas used to calculate body density. As in many situations, the formula itself is a predictor that is based on a sample population, under which the person being tested may not fall, as well as the formula using other inaccurate body fat testing methods to establish a base. In addition, inaccuracies can arise due to hydration levels.

As a spot body fat predictor, the skinfold method can have very significant inaccuracies, which studies have shown can be up 10-15%. For changed over time, this method fairs somewhat better and studies show an error rate of up to 5%

http://weightology.net/weightologyweekly/?page_id=250


Calculators Based on Measurements

Calculators, such as the military body fat estimator, use a number of body measurements and your weight and height to estimate body fat %. The accuracy of these is dependent on a number of factors, including: how accurately you measure, how closely your body type and composition resembles the sample used for the formula and your body fat distribution. For some people they can be very off, for others they can give a pretty good estimation. They are a free and relatively decent was to track progress, assuming your fat comes off proportionately across your body, which we all know does not usually happen.

Examples can be found here: http://www.fat2fitradio.com/tools/

The Mirror/Eyeballing

To be honest, this is probably as accurate a measure as most of the above assuming you have a good idea as to body composition and the related BF%.




At the end of the day it is really kind of irrelevant what your exact body fat % is. It is a tool, nothing more, to assess whether you are in a healthy body fat range and to assess progress, which can easily be done by looking in the mirror and taking measurements. There are circumstances where it is more useful than others. For example, people will use estimated body fat percentages to determine whether to start or finish a bulk as well as to determine how successful the bulk was at increasing LBM.


So, in summary, if you have one near you and can afford it, hydrostatic testing appears to be the best method, both for a spot BF% and to assess progress, which can be combined with seeing progress in the mirror or on a tape measure.