The Ultimate Body Fat Testing Guide

The Ultimate Guide to Body Fat Testing (FI)

The human body has a variety of classifications that can be placed upon it, such as the fact that there are 206 bones, ~640 muscles, and 78 total organs (five of them vital) in the human body, but the classifications which will be discussed in this article relate to body-weight (BW), lean body mass (LBM), percent body fat (PBF), and other body tissue classifications.

There are a variety of ways to determine your body composition, and as a result, your body fat percentage, and this article will endeavor to examine the different testing methods currently available, the pros and cons of each method, provide a final recommendation as to which methods are the best overall, and some general tips to follow when testing your body composition.

Lean body mass (LBM) and percent body fat (PBF) can be determined a variety of ways, ranging from free and easy, to expensive and complicated, but the most accurate results come from the methods which, you guessed it, are relatively expensive and complicated. Luckily, usually the complicated part of different body composition tests has been reduced in simplicity for the user to a printed out sheet of paper. Let’s learn about the different body composition testing methods, starting with the simplest scientifically, and ending with the most complex.

Photos and/or Mirror

Photos and/or the mirror is the first weapon in your arsenal of body composition testing techniques. Using both photos and the mirror have no strong scientific basis backing them up, as they are purely anecdotal and subjective based on how the viewer perceives it, but for a day to day, or week to week body fat percentage check, photos and the mirror can be surprisingly useful.

Taking progress photos is something you should already be doing to track yearly progress, and these can be useful in tracking body fat percentage changes over time. The mirror is more useful for developing a day to day sense of how your body is changing, either through gaining or losing both lean body mass and body fat.

Builtlean BF Comparisons


Courtesy of

I’m sure you’ve seen the above graphics from BuiltLean, and while helpful, they are not accurate for a few reasons. First, each photo is of a different person (except for one guy who is represented twice at 25 and 30% bodyfat), and since everyone has different heights, muscle insertions, bone structures, and other body variables, you cannot use photos of different people at seemingly various body fat percentages to make an estimate of your own body fat percentage. Second, the angles, lighting, skin color, and posture of each person is different, and these can have a big effect on what your body fat percentage actually looks like in person as well as in a photo. Third, depending on the amount of lean body mass you have, your body fat percentage might look different than you might expect. Let me explain.

Photos and the mirror can be misleading for the above reason because if you add LBM and PBF, you might look more cut as a result of your increased muscle mass, but in fact you might have a higher PBF percentage than you previously did! Using myself as an example, as I have gotten bigger, going from 6′ 145 lbs to 6’1″ 195 lbs, I have put on a ton of muscle and as a result look a lot better at higher body fat percentages than I used to, on account of my increased muscularity, but my PBF has increased overall.

It is for the above reasons that I do not recommend using the mirror and/or photos as a way to accurately estimate your body fat percentage. Photos and the mirror are great as a subjective tool in assessing your body fat percentage though.

Photos and/or Mirror Pros and Cons


  • Free
  • Easy and anyone can do it
  • Fast
  • Can be used to gauge long term and short term progress


  • Highly subjective
  • Is dependent on variables such as lighting, skin color, posture, etc
  • Adding muscle as well as fat can lead to deceiving body fat percentage change results
  • Does not account for water weight, bloat

Lean Body Mass (LBM) Equations

Derived in 1966, an equation was developed by R. Hume from the Department of Medicine, Southern General Hospital, Glasgow which predicts the lean body mass (LBM) of a person from their height and weight (full PDF). Hume used 29 men and 27 women to test his equation, and he was able to develop separate equations accurately predicting the LBM of both men and women which had multiple correlation coefficients (R) of 0.96 and 0.83 respectively*.

In layman’s terms, the equations he developed are very accurate for the average man, and fairly accurate for the average woman. Unfortunately for those into fitness and strength sports, we are not really average, at least not body composition wise, so take the results of these equations with a grain of salt. Also, with obesity on the rise, and body fat percentage rising as a whole (and consequently, LBM falling), this equation is likely to be less accurate nowadays. Since Hume’s original equation, dozens of other LBM equations for various population subsets have been developed, but they are still only accurate when testing across a population sample size.

The equations developed by Hume are:

For men : LBM = (0.32810 * W) + (0.33929 * H) – 29.5336

For women : LBM = (0.29569 * W) + (0.41813 * H) – 43.2933

Where W is body weight in kilograms and H is body height in centimeters.

Once LBM is determined, proceed with the following equations to determine body fat percentage:

BF = Total BW – LBM 

PBF = BF / Total BW

There are other equations out there which can be used to predict your LBM, PBF, or BMI, but for our purposes, this method of body fat testing is too inaccurate to delve into further.

*Note – The Multiple Correlation Coefficient, R, is a measure of the strength of the association between the independent (explanatory) variables and the one dependent (prediction) variable, in this case, actual LBM of a person and their predicted LBM via the equation. A R value of zero implies no linear relationship, and a R value of 1 implies a perfect linear relationship (between the two values). The closer to one R is, the more statistically significant it is.

LBM Equation Pros + Cons


  • Free
  • Easy
  • Fast


  • Requires accurate height and weight measurements
  • Inaccurate, does not take into account variables outside of height and weight (such as lifting objects against the force of gravity)
  • Cannot be used to accurately track progress, because as your height will stay the same (as long as you are an adult), your LBM and PBF ratio will just increase proportionally instead of taking into account muscular gains or body fat loss

Body Fat Calipers

Calipers-compressorBody fat calipers are another tool you can use in your quest to determine your body fat percentage. Body fat calipers are likely the most popular tool used to test ones percent body fat, and body fat calipers are fairly cheap as well!

Body fat calipers measure skinfolds to calculate the amount of subcutaneous fat a person has. The skinfold measurements are then input into an equation to predict the body density, percent body fat, and lean body mass.

I bought the Accu-Measure Body Fat Caliper when I first started lifting, and it has held up remarkably well. The nice thing about the Accu-Measure is that it has a knob that you press when taking your measurement, and once it clicks into place, you know you have applied enough pressure to take your reading. With traditional body fat calipers, the act of applying the right amount of pressure to take an accurate caliper reading is what takes the longest to learn, so removing that learning curve allows the average person to start taking accurate measurements instantly.

One thing to note with plugging in your skinfold measurements into an equation is that there are dozens of different body fat caliper equations which have been developed for a variety of reasons. Same as the LBM equations, different ethnicities, men and women, athletes and sedentary populations all have different equations, so it is important that if you do use an equation to calculate your PBF using calipers, that you follow these two rules:

  1. Do not take the PBF value that was calculated from your measurements as gospel. As stated before, depending on the equation used, it can inaccurate by a wide margin, either underestimating or overestimating your PBF.
  2. Use the same equation each time. This enables you to accurately track changes in your PBF, even if the actual PBF number is wrong

A method to work around some of the accuracy limitations in testing your PBF using calipers is to not use an equation at all, but instead keep track of your various skinfold measurements and monitor how they change over time. These measurements, combined with a mirror and a scale, can provide a very accurate way of determining the change in your PBF, but not your actual PBF.

If you are going to test your percent body fat with calipers, it is also worth noting that it is best to eliminate as many variables as possible leading up to each time you test. To eliminate these variables, just make sure that you test under the same conditions each time, for example:

  • Have a meal at the same time before each time you test, or better yet, perform each test upon waking up as you have fasted for the past 6-8 hours.
  • Consume the same amount of water before each time you test, or again, perform each test upon waking up.
  • Take each test at the same time.
  • Preferably do not test immediately after exercise.

A few more recommendations for testing your PBF using skinfold calipers:

  • All measurements should be made on the right side of the body.
  • The ends of the caliper should be held 1 cm away from thumb and finger, placed perpendicular to the skinfold, and  measurements should be taken halfway between crest and base of skinfold.
  • Maintain pinch while taking a measurement.
  • Take each skinfold measurement within 1-2 seconds after applying the body fat calipers to the skinfold. If you delay in taking your measurement, your skinfold measurement will be underestimated.
  • Measure yourself in the exact spots recommended. If your test requires you to test exactly 1 inch to the right of the belly button, then grab a tape measure and mark it out with a sharpie, do not guess! Repeat this process for each test to ensure accuracy across tests.
  • To ensure accuracy of measurements, take duplicate measures at each site. If the duplicate measurements are not within 1 to 2 mm of each other, retake those measurements.
  • Give your skin and fat time to regain their normal shape and thickness in-between measurements by rotating through test sites.

If using calipers to test your PBF, I recommend using the seven site equation which you can use at ExRx.

Body Fat Calipers Pros and Cons


  • Cheap one time purchase
  • If you buy the Accu-Measure Body Fat Caliper it’s relatively easy
  • Fast
  • Can be used to gauge long term and short term progress
  • Provides concrete measurement data which can be used to track changes in PBF over time


  • Can be used with dozen’s of different equations, which can complicate the process
  • Relatively inaccurate at estimating your true body fat percentage
  • For increased accuracy, body fat caliper testing requires you test in the same spots each time, and this can be difficult to do if you loose or gain a lot of fat

Overall, body fat calipers are the best combination of cost-effective, fast, easy, and accurate when it comes to testing your body fat percentage out of the currently available options.

Bioelectrical Impedance Analysis (BIA)

inbody-compressorBioelectrical impedance analysis (BIA) is another quick and easy way to determine you percent body fat, but it comes with a few caveats.

Bioelectric impedance analysis (BIA) works placing your body in contact with electrodes (usually touching your feet and hands), and then running an unnoticeable electrical current through your body. By determining the resistance of a current running through your body, it is theoretically possible that an estimate of your LBM and PBF is possible. As the machine runs the electrical current through your body, it measures the drop off of current that occurs, which is due to the natural resistance of your body. For body tissues, water plays a large role in how the electric current travels through your body. Water offers very little resistance to electric currents which travel through it, so the higher percenetage a body tissue is composed of water, the less resistant that well hydrated tissue will be.

According to the BIA tests I have done, water accounts for about 3/4 of the total weight of your lean body mass, with dry lean mass accounting for the other 1/4, so LBM contains a lot of water. Body fat on the other hand contains very little water, and as a result, body fat has a high resistance, while lean body mass has a low resistance. The biggest flaw of bioelectrical impedance analysis testing is the accuracy of the method. All of the above science sounds fantastic until you examine it in close detail. To start off, if you remember from physics, an electrical current always follows the path of least resistance, and this applies to your body too. If you have a large amount of adipose tissue (fat), the current running through your body will avoid a lot of the adipose tissue as it has too high of a resistance, and after analysis, your PBF will be calculated lower than it actually is.

This is in fact one of the biggest issues concerning the bioelectric impedance analysis method, which is that it almost always calculates results with your PBF being lower than it actually is. Hypothetically, for someone who is actually at 12% body fat, a BIA machine might test you at 8%, which is a huge difference!

There are a few other considerations to take into account as well when testing your body composition with BIA, and when you read the instructions for these BIA machines, they often mention the following variables:

  • Body fat measurements are lower when taken shortly after eating a meal, which can cause variations between the highest and lowest reading of PBF taken throughout the day by up to 4.2% of body fat.
  • Exercise before taking a BIA test can lead to an overestimation of LBM and an underestimation of PBF as a result of decreased body resistance.
  • Dehydration also affects BIA measurements as it increases the electrical resistance of the body through the reduction of water. As a result, BIA tests will interpret less LBM and more body fat, and this effect has been measured to be able to cause a 5 kg underestimation of LBM and an overestimation of body fat.

With these variables affecting the results of BIA tests, it is advised to use the restroom before testing, to not eat or exercise before testing, to take the test in the morning, to stand upright for 5 minutes before the test (to evenly distribute bodily fluids), and to remove any items from your pockets for the duration of the test.

There are a few different types of BIA machines, but they generally come in 2, 4, and 8 electrode varieties. The two electrode BIA machines (typically foot-to-foot) are less accurate than the four electrode BIA machines and the eight electrode BIA machines (feet-to-hands). Overall, BIA test results will generally show that you have a lower PBF than you actually do, and a higher LBM than you actually do as a result. This is a limitation of the technology and is unlikely to drastically change in the future.

Other than the negative of poor accuracy, which affect most body composition testing methods, BIA tests are quick and easy to take, and as long as you eliminate as many of the variables listed above as possible for each test you take, BIA tests are very well suited in measuring changes in body composition over time for individuals. I personally can attest to this as so far I have taken three different BIA tests, all under consistent variables, and the test results coincide with my personal observations I have made concerning my changing body composition.

Bioelectrical impedance analysis Pros + Cons


  • Very easy to take, as long as you have access to a BIA machine
  • Very fast, takes less than 5 minutes
  • Well suited to tracking body composition changes over time
  • If done at a gym which owns the equipment, most BIA tests are free


  • If not taken at a gym, BIA test can cost more than they are worth
  • BIA tests are not well suited to taking a single, accurate body fat percentage measurement
  • Due to the science behind BIA tests, results are often skewed towards lower PBF and higher LBM

Hydrostatic Body Composition Analysis

hydrostatic-weighing-getting-tanked-photo-smaller-compressorHydrostatic body composition analysis, used to be the most accurate way to determine your body fat percentage, only recently having been supplanted by DEXA scans. Hydrostatic testing is still a viable option for determining your body fat percentage, and since hydrostatic testing has been around for a while, it is easier to find places which offer the service than DEXA scans.

Hydrostatic body composition testing measures the density (mass per unit volume) of your body and then uses specially developed equations to determine your fat and fat-free mass. You fat-free mass includes water, muscle, organ, skeleton, and all other body tissues other than fat. The two main equations used are:

Siri (1956): Fat % = [4.950 /Density – 4.500]×100

Brozek et al. (1963): Fat % = [4.570 /Density – 4.142]×100

One of the issues with hydrostatic testing is that the density of your fat-free mass can vary depending on your ethnicity, and if this is not taken into account your body fat measurement can be inaccurate. This, along with other sources of error can mean your individual results are off by as much as 5-6%. Hydrostatic testing is great for tracking the body composition of a population, given the right equations are used, as much of the errors are averaged out through the larger sample size, but it is still one of the more accurate body fat testing methods available for individuals.

Hydrostatic body composition analysis tests are one of the more intensive and difficult methods used to test your PBF, and as such I do not recommend you get a hydrostatic body fat test if you have the ability to get a DEXA scan, which is much easier and more accurate. Hydrostatic testing requires you to submerge yourself completely underwater while sitting on a scale, siting as steady as possible for an extended period, all while a measurement is taken. Additionally, any air in your body or trapped in your swimsuit effects your results, so you have to get as much air out of your swim suit as possible and blow out as much air from your lungs as possible, all with your head underwater. Considering the difficulty of the test, multiple measurements often need to be performed in order to collect a good density measurement.

Sources of error can include air still trapped in your suit, air leftover in your lungs, air and food in your digestive tract, and the usual sources of error which can be avoided such as increased hydration intake prior to the test and exercise before the test.

Hydrostatic testing can often be scheduled through your local university or healthcare facility, and hydrostatic testing also is commonly scheduled at Crossfit gyms where they bring a mobile hydrostatic testing unit on site. You can also find good deals on hydrostatic testing on Groupon. Hydrostatic body fat testing will usually cost anywhere from $30 to $100.

Overall, the combination of discomfort, price, and inaccurate is too great for me to enthusiastically recommend taking a hydrostatic test to determine your body composition, especially since DEXA scans are more accurate, the same price, and much easier/faster.

Hydrostatic Body Fat Testing Pros and Cons


  • One of the more accurate methods available to test your body fat percentage
  • Is commonly scheduled at Crossfit gyms


  • Expensive
  • One of the slowest testing methods available
  • Can be uncomfortable
  • Not as accurate as other comparable methods (DEXA)

Dual-Energy X-ray Absorptiometry Testing (DEXA)

Dual-energy x-ray absorptiometry (DEXA, or DXA) is currently the most accurate method of testing your body composition. DEXA scans were originally developed as a way to determine bone mineral density, as DEXA scans have since been used to measure body composition.


To take a DEXA scan, you lie on your back and the machine makes a single pass over your body to collect the required data.

DEXA scans are able to calculate your body composition by using x-rays and their reduction in strength as they pass through various body tissues such as bones, muscle, and fat. Dense body tissues such as muscle absorb more x-rays than less dense body tissues such as fat, and it is the reduction of x-ray strength from the source to the receiver that allows for body composition to be determined. DEXA machines utilize x-rays from two different sources, which when used together, greatly improve the accuracy in calculating body composition. Since DEXA scan results are determined from thousands of x-ray scans, DEXA scans are able to accurately determine overall, as well as regional, body fat, lean body mass, and bone mass percentages.

The one drawback with DEXA scans is that they measure visceral fat as well as subcutaneous fat and then lump these measurements together for your total body fat percentage. As a result, an athlete at a lean 10% subcutaneous fat will have a higher PBF measurement with a DEXA scan, such as 15-18% overall body fat. To take your DEXA scan results and translate them into the percentages that are typically used, subtract 5-8% depending on how you’re built to get your subcutaneous body fat percentage.

You can often schedule a DEXA scan through your local university, or a lot of healthcare facilities have DEXA units for use in determining bone mineral density and body composition. Groupon also has a ton of deals on DEXA scans, but probably only if you live in or near a large urban area. DEXA scans typically cost anywhere from $50 to $100.

As with other body fat testing methods such as hydrostatic testing and BIA, it is best to comply to the following guidelines before taking a DEXA scan:

  • Fast before the test
  • Do not exercise before the test
  • Do not drink excess water before the test
  • Use the restroom before the test

Since DEXA scans do use x-rays to determine your body fat percentage, you will be exposed to radiation during the test, but the amount is quite minimal. Below are some radiation exposure amounts from common events compared to a DEXA scan:

Radiation Exposure (in sieverts) Source
0.1 uSv Eating one banana. Bananas are slightly radioactive because of their potassium. Many foods contain trace radioactive elements occurring naturally
0.25 uSv Airport security screening
0.4 uSv BodySpec full body composition DXA scan
1 uSv Using a CRT computer or TV monitor for a year
10 uSv Background radiation received by an average person over a normal day. This comes from cosmic rays, the Earth’s crust and soils, buildings, food, and medical scans
40 uSv Round trip flight from New York to LA
1.5-1.7 mSv
(1,500 – 1,700 uSv)
Average annual dose for flight attendants
5-6 mSv
(5,000 – 6,000 uSv)
A chest CT scan
50 mSv
(50,000 uSv)
Annual dose limit for nuclear power plant workers
1 Sv
(1,000,000 uSv)
Measured in water leaking from Fukushima No. 2 reactor over one hour. Direct exposure at this level causes symptoms such as nausea and decreased white blood cell count, but not immediate death. However, exposure at this level is correlated with increased risk of future death from cancer
6 Sv
(6,000,000 uSv)
Typical for Chernobyl workers who died within a month.
Courtesy of

DEXA Testing Pros and Cons


  • The most accurate method of determining your body composition currently available
  • Due to the nature of the testing, can measure overall and regional body composition
  • Quick and easy


  • Expensive
  • Can be difficult to find a testing location
  • Accounts for visceral and subcutaneous body fat, making it hard to compare to the results of other methods

Overall, DEXA scans are the most accurate way to test your actual body fat percentage. Results from a DEXA scan can be interpreted from a single measurement, and do not require multiple measurements over time to accurately measure your PBF such as body fat calipers and BIA.

Which Method of Body Fat Testing is Best?

Of the body composition methods covered, LBM equations, photos and/or mirror, body fat calipers, bioelectrical impedance analysis (BIA), hydrostatic, and dual-energy x-ray absorptiometry (DEXA), there are a few winners and losers in various categories.

When it come to the best combination of ease of use, price, and accuracy in regards to body composition, body fat calipers win narrowly over BIA. Hydrostatic and DEXA body fat testing methods are too expensive to perform consistently, and are better at supplementing any collected body composition from body far calipers and BIA tests with accurate body fat percentage data. The body fat caliper I prefer, and the most accurate for the average gym-goer is the Accu-Measure Body Fat Caliper, and it is so cheap it is kinda crazy not to own one if you are serious about working out.

When it comes to the most accurate method of determining your body composition, DEXA scans win, with hydrostatic testing coming in a distant second place. DEXA scans are able to measure overall and regional trends in body fat, LBM, and bone mass, and they cost roughly the same as hydrostatic testing.


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Stefan Burns

Stefan Burns

Fitness, nutrition, and powerlifting buff. Created Strength Cooperative as a way for hardworking, natural lifters to share advice on how THEY got results in the gym.
Stefan Burns

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