If you work with clients face to face, you’ll find one consistent trend – people want results and to track their progress. And one of the best ways to do this is by measuring their body fat percentage. As a trainer, you can use this as a tool to help your clients reach their goals.

Many high-performing humans are consistently driven by a desire to improve. “How can I get better today?”

You’re the linchpin in this scenario. You have the tools to promote systematic improvement through physiological adaptation. You understand how this works from a biochemical perspective, but your clients can’t always see that.

So, you have to distill the science down into something meaningful for them. Body composition is usually the easiest metric that everyone understands – higher numbers are not ideal, and lower numbers are better, at least from a long-term health perspective.

Recap of Part 1 of This Body Fat Percentage Measuring Series

Thus, we need to understand how to accurately measure body composition for anyone you might encounter. Part 1 walked you through everything that influences water retention and cellular swelling.

If you don’t have time to read back through Part 1, this simple synopsis will get you started with body fat percentage measurements for both your clients and yourself:

Many lifestyle and nutritional factors play a role – regardless of how large or small the impact, the most important thing to remember is: BE CONSISTENT.

If you decide to have two meals and a half-gallon of water before testing, you need to have a half-gallon of water and two meals in your system the next time you test. If you’re confused by all the variables and can’t seem to decide the best time/conditions to test under, simply test first thing in the morning upon waking when you have nothing in your system (food or water).

Give yourself the best chance for a consistent reading by following this checklist before your next skinfold measurement:

  • Always test before training.
    • If possible, test at least 36-48 hours after training to allow the inflammation to subside and glycogen levels to replete.
  • No alcohol for at least 3 days prior.
  • Keep carbohydrate intake consistent for at least 7-10 days prior.
  • No major water and/or electrolyte manipulations for at least 24-48 hours prior.
  • Take subsequent tests at the same time of day as the first test.
  • Ensure similar feeding times and number of meals before testing.
  • Maintain a normal skin texture (no creams, oils, etc.) and ensure the muscles are relaxed.
  • Mark skinfold sites to ensure reliability with each subsequent reading.
  • Don’t start using creatine between different tests – either start using it before your first measurement or don’t use it during any of the following tests.
  • Take all measurements on the right side of the body for consistency.
  • Use multiple measurements at each site and ensure the same individual conducts all the tests to ensure reliability between trials.

Skinfold Science Made Simple

Take a minimum of 2 measurements (ideally 3), and if they vary by more than 2mm or 10%, take an additional body fat percentage measurement. Mark all folds with a washable marker so that they are easy to locate for the second and third measurements. Use a “t” to designate the location – the horizontal line provides a point of reference for your pinch, and the vertical piece provides guidance on the direction of the fold.

Here’s a list of all the site-specific locations and their corresponding folds:

  1. Chest (diagonal fold)
  2. Men: Halfway between the armpit and the nipple.
  3. Women: 1/3 of the way between the armpit and the nipple.
  4. Abdominal (vertical fold): 2cm to the right of your belly button.
  5. Suprailiac (diagonal fold): Crest of the hipbone directly below the front of the armpit.
  6. Midaxillary (vertical fold): Directly below the middle of the armpit at the level of the breast bone (sternum).
  7. Tricep (vertical fold): Halfway between the top of the shoulder (acromion process) and the point of the elbow (olecranon process).
  8. Subscapular (diagonal fold): From the medial border of your scapula closest to your spine to the bottom (inferior) border.
  9. Thigh (vertical fold): Halfway between the crest of your hip bone and the top of your kneecap.

Assess, Don’t Guess Body Fat Percentage

Want the most accurate measure of progress? Stick with the 7-site method. If you’re really interested, there’s even a 12-site method you can use, but I don’t cover it in this article.

Feeling overwhelmed by all the details, or perhaps you want a view of the big picture?

Stick with the 3-site method. It’s not as accurate, but it can keep you on track and provide a valuable measure of progress.

I’ve provided 2 formulas for the 3-site method because each offers a different perspective on your current body fat percentage. Also, certain skinfolds are impossible to perform on yourself due to their location, such as the tricep and subscapular. When measuring yourself, use the first 3-site measurement formula.


  • 3-Site: 1.10938 – 0.0008267*(X1) + 0.0000016*(X1)2 – 0.0002574*(X2)
  • 3-Site: 1.1125025 – 0.0013125*(X3) + 0.0000055*(X3)2 – 0.0002440*(X2)
  • 7-Site: 1.112 – 0.00043499*(X4) + 0.00000055*(X4)2 – 0.00028826*(X2)

X1 = Sum of chest, abdomen, and thigh skinfolds.

X2 = Age in years.

X3 = Sum of chest, triceps, and subscapular skinfolds.

X4 = Sum of triceps, abdominals, suprailiac, thigh, chest, subscapular, and midaxillary skinfolds.


  • 3-Site: 1.0994921 – 0.0009929*(X1) + 0.0000023*(X1)2 – 0.0001392*(X2)
  • 3-Site: 1.089733 – 0.0009245*(X3) + 0.0000025*(X3)2 – 0.0000979*(X2)
  • 7-Site: 1.097 – 0.00046971*(X4) + 0.00000056*(X4)2 – 0.00012828*(X2)

X1 = Sum of triceps, suprailiac, and thigh skinfolds.

X2 = Age in years.

X3 = Sum of triceps, suprailiac, and abdominal skinfolds.

X4 = Sum of triceps, abdominals, suprailiac, thigh, chest, subscapular, and midaxillary skinfolds.

Men vs. Women

When it comes to manipulating body composition and measuring body fat percentage, we have to remember that hormones run the show. Everything in your body is dictated by a complex interplay of hormonal cascades that feedback on each other with both positive and negative inputs. Sometimes, a picture is worth a thousand words…

Measuring body part percentage

Are you confused yet?

Yeah, same here. Endocrinology, a branch of medicine concerned with the structure, function, and disorders of the endocrine glands, is a never-ending system of loops that essentially governs every single process in your body.

However, the important thing to note is that men tend to have fairly consistent hormonal levels across the course of the day, week, and month.

On the other hand, women tend to have much larger hormonal swings throughout their menstrual cycle as estrogen, progesterone, LH (luteinizing hormone), and FSH (follicle-stimulating hormone) all fluctuate.

Now, this cycle is obviously necessary when it comes to reproductive function and general health. But people often forget that multiple hormones change during this cycle, not just the four listed above. Remember how I mentioned that every hormone feeds back on something else positively or negatively? Well, the same thing applies here. Those four hormones play a role in multiple symptoms. Thus, many people see changes in performance, weight, water retention, bloating, swelling, appetite, and a whole host of other issues.

Suffice it to say, without getting too deep into the science of the endocrine system, your weight will probably change randomly throughout your cycle. Thus, it could be beneficial to track your cycle alongside your weight for a month or two and monitor any associated changes.

If you want to go the extra mile, graph your weight against the days of the month along a simple axis, and note any spikes during the 20-35 day cycle. I’ve found this helpful for my clients.

Once you’ve done this for a month or two, you may be able to determine in what phase of the cycle your weight spikes and how long it takes to return to baseline.

Realistically, I’ve seen some clients gain 1-5lbs during certain phases of their cycles. But their weight usually returns to normal in the following days because it was merely fluid shifts and not actual tissue accrual. This assumes they stayed on track nutritionally.

If you’re not that interested in going down the rabbit hole, just remember this: At some point during your cycle, your weight may jump due to changes in water retention, stress hormones, and nutritional factors, mainly electrolytes and water intake. However, don’t stress about it because this will only prolong the retention of any water. It’s simply a normal part of your cycle, and this too shall pass.

Testing Frequency

If you’re like most, you want results, and you wanted them yesterday. No one can fault you for that because progress and enjoyment are usually the sustaining forces that build habits.

However, when it comes to body composition changes, things often don’t move as quickly as people hope.

As a general rule of thumb, it’s probably best to measure fat percentage once every 8-10 weeks to assess changes. Fat loss tends to occur much more quickly than muscle growth, so keep that in the back of your mind when taking measurements.

Physiological changes in muscle growth usually take at least 2-3 weeks to catch up to the current training phase. So, if you’re working through an exceptionally high-volume block, don’t expect to see any massive changes to the scale until you’ve completed a few weeks of the program when your physiology has had a chance to adapt.

A Quick Note on Muscle Growth and Fat Loss…
Muscle growth is a MUCH more difficult process than fat loss, so the time frame for progress needs to be expanded.

For example, you can lose roughly 0.5-1% of your body weight in fat mass weekly. This translates into 1-2lbs of loss per week for a 185lb individual.

However, muscle growth tends to exhibit a more negative exponential regression. In other words, you tend to gain more muscle when you start training than 5, 10, or 20 years down the road when the rate of muscle growth slows significantly.

From a graphical perspective, it would look like this. The y-axis is the total number of pounds accrued each month, and the x-axis is the number of months spent training:

Look from low body fat percentage

When you first start training, you can probably add 2lbs of muscle each month (20-25lbs/year). In your second year of training, this drops to 1lb per month (10-12lbs/year). In your third year, this drops again to 5-6lbs of total muscle for the year. And as you approach 4+ years of training, you’ll be hard-pressed to amass more than 3-5lbs of muscle per year.

NOTE: For women, cut all the above numbers in half. Women tend to have a harder time accruing and supporting large amounts of muscle mass simply due to hormonal and physiological differences. However, don’t despair ladies. Fat loss tends to be fairly similar among men and women, so you can still have a fantastic body composition.

Natural Athletes

Now, this entire discussion relies on the fact that we’re discussing natural athletes. If you choose to use external hormones to enhance muscle growth or fat loss, these timelines go out the window because your physiology is running at warp speed.

However, if you’re considering going the PED (performance-enhancing drug) route, a word of caution. Unless you plan to compete at an exceptionally high level (aka nationals or worlds) in powerlifting, strongman, or bodybuilding, I strongly discourage you from using any compounds that influence endocrinology. Unless you have an exceptionally smart and well-read endocrinologist on your team who will run labs on you every 10-12 weeks, you will put yourself at risk for permanent damage to multiple organ systems. Know that these endocrinologists are few and far between when it comes to PED use and athletic enhancement.

Sizing Up the Body Fat Percentage Sums

Remember that with all data points, there will ALWAYS be a standard margin for error. For calipers, it’s generally 3-5%, so take your body fat percentage results with a grain of salt. Therefore, don’t hold too tightly to them because they are fairly transient and highly dependent upon a vast number of factors.

If the data changes positively, keep pushing, and don’t change much. But if you see a negative trend, examine all the factors above and see if they’re contributing to poor reliability between measurements. If not, tweak some aspects of your training and nutrition before reassessing.

Nothing will be perfect, but with objective data, it will be much easier to measure progress and modify training to produce the desired results.

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