Determining Natural Bodybuilding and Arm Size Potential

Determining Natural Bodybuilding and Arm Size Potential

Muscle mass and big arms.

Everyone wants to look like a freak. Few achieve this level. Yet if you believe what you read on the Internet, a ripped pair of 20-inch guns and a 240-pound lean physique are as common as black t-shirts at a death metal concert.

Let's be real here for a moment.

I do not care what stories you hear at the gym, or on the Internet. Lean 20-inch natural arms are not going to happen unless you have gigantism. And a ripped 240-pound physique? You live in a fantasy world if you believe this is possible with steroids.

Related: Hard and Heavy Arm Building Workout Program

And no, I am not talking about the 20-inch arms you find on the 320 pounds "husky" guy who believes within the bowels of his soul that he is really 15% body fat. Nope, sorry dude. You are still 42% body fat.

I am talking about guys that are legit 10 to 15% body fat. Men that have spent years toiling away with the iron, and have not only built impressive arm size and muscle mass, but also have the definition and vascularity to back up their lean condition.

Lean 17-inch arms are the crowning glory for the average natural lifter. So is a ripped physique in the 180 to 190 pound range. With this in mind, the question becomes:

How big can I expect my body and arms to get naturally?

Let us take a look at what the research has to say, and explore natural arm size and muscle mass potential.

Natural Lean Mass Potential


When it comes to natural bodybuilding potential, and natural arm size potential, Dr. Casey Butt is the king of research. Casey conducted the most extensive study ever performed on true natural bodybuilders.

The stats of 300 top natural bodybuilding champions were analyzed. These elite naturals competed between the years of 1947 to 2010. It cannot be overstated this data pool featured the best of the best; the genetic elite. Therefore, the resulting numbers provide us with not just muscle growth and arm size standards, but standards to be the best of the best.

Dr. Casey Butt studied bone structure, body fat percentage, height, lean body mass, and wrist and ankle size. From this data, the following formula was derived to determine just how much muscle mass a male natural bodybuilder could add to his frame.
Lean Mass

Variables for Dr. Casey Butt's formula are:

H = Height in inches
A = Ankle circumference at the smallest point
W = Wrist circumference measured on the hand side of the styloid process. (The styloid process is the bony lump on the outside of your wrist.)
%bf = The body fat percentage at which you want to predict your maximum lean body mass

It should be noted that this formula is most accurate for lifters with a reasonable body fat percentage. Blow up the scale with body fat, and you will likely blow up the formula too.

Bone structure plays a role too. Outliers with very unusual bone structures, either small or large, will probably find the results of this formula to be inaccurate. There simply are not enough super small or super large bone structures in this champion data pool to appropriately calculate the mass potential for fringe body structures.

With that said, men with moderately small bone structures will be lucky to come within 95% of their lean body mass predictions. It is hard enough for the genetically elite to maximize potential. Those with a smaller bone structure tend to be weaker (tend - this is not a rule but an observation), making it harder to pack on strength and size.

Conversely, men with wider bone structures and hips may be able to exceed these predictions by 5%. They will have a slightly easier time building strength, and their frame will also carry around a bit more muscle mass.
Natural Bodybuilder

Steve Shaw's Natural Bodybuilding Potential Formula

While this formula is quite complicated, I have simplified it a bit over the years. My variation streamlines Dr. Casey Butt's formula while only sacrificing a very minor degree of accuracy.

Basically, a 5'10" lifter has the potential to pack on 178 to 180 pounds of lean body mass. This is the weight if you had absolutely zero body fat. Obviously, this is impossible. You would be dead if you had no fat. Still, this number helps us to calculate a reasonable weight goal for body fat percentages ranging from 10 to 40%.

For every inch above or below this height, add or subtract 4 to 5 pounds of lean body mass, respectively.

The following chart compares the maximum lean body mass potential, body fat percentage, and overall weight.
Height LBM (No Fat) 10% 15% 20% 25% 30% 35% 40%
5'4"  153  170  180.5  191  204  219  235.5  255
5'5"  157.5  175  186  197  210  225  242.5  262.5
5'6"  162  180  191  202.5  216  231.5  248  270
5'7"  166.5  185  196.5  208  222  238  256.5  277.5
5'8"  171  190  202  214  228  244.5  263.5  285
5'9"  175.5  195  207  219  234  251 270  292.5
5'10"  180  200  212  225  240  257.5  277  300
5'11"  184.5  205  218  231  246  264  284  307.5
6'0"  189  210  223  236  252  270  291  315
6'1"  193.5  215  228.5  242  258  276.5  298  322.5
6'2"  198  220  235  248  264  283  305  330
6'3"  202.5  225  239  253  270  289.5  312  337.5
6'4"  207  230  244.5  259  276  296  319  345

I want to stress that this chart is meant to be used as a goal and a guideline, not a restriction. With that said, many lifters have a hard time dealing with the reality that you can only get so big naturally.

It can't be stressed enough that this data was collected using 300 of the greatest natural bodybuilders ever. The best of the best. Most lifters won't get within 5 to 10 pounds of their natural potential. Even if they do, it becomes harder to maintain that mass when you are aiming for a body fat under ten percent.

Many young guns hit the gym running and pack on a fast 10 to 15 pounds of muscle. They get cocky and assume this rate of gain is sustainable. It is not. You must realize this.

I receive so many questions from men and women who believe they have reached plateaus. Frustration sets in. Most times what they are experiencing isn't a plateau at all. It is a natural slowing of the muscle-building process. You cannot build 10 to 15 pounds of muscle each year, every year. If this was possible everyone would look like Mr. Olympia.

Most of these folks are still gaining, but they think they are doing something wrong.

They are not.
Male Female

Continue to monitor arm and leg size measurements and bodyweight. Understand that while rates are slowing, you are not doing anything wrong at all. In fact, what you are doing is likely producing gains and is actually what you should be doing.

Don't panic. Don't be quick to jump ship on a workout program or eating style that had been yielding results. You know how to build muscle and strength. You still do. Now, it is a long game. get patient, dig in, and monitor changes in progress over months and months, not weeks.

The rate of natural muscle gain decreases by about 50% from year to year. The average male can expect to gain about 16 pounds of muscle during his first year of lifting. Few reach this level, but it is certainly a reasonable goal if you are lifting properly and eating right.

With that said, here are some good expectations for men during their first five years of muscle building:
  • Year 1 - 16 pounds
  • Year 2 - 8 pounds
  • Year 3 - 4 pounds
  • Year 4 - 2 pounds
  • Year 5 - 1 pound
Over the course of their life, a natural male can expect to gain about 30 to 35 pounds of muscle in total. This is assuming they are not beginning their lifting career underweight, to begin with.

For example, if you are 5'10" and only 130 pounds you have the potential to add more muscle than this. Why? Because your body is not carrying around a "normal" amount of muscle mass. It is underweight. Therefore, you may gain 20 to 30 pounds of size before these numbers apply to you.

Remember that this size isn't just muscle. It includes skin, bone, etc.

How much muscle can a woman expect to gain over the course of the same 5 years? Good question. There is not much research on this subject.

For the average woman, I would say that a 12-pound muscle gain over the course of four to five years is substantial and reasonable. I would also add that most woman do not want more muscle mass than this anyway. Even a 5 to 8 pound addition would make the average female look fit, firm, and sexy.

Breaking this down over a five year period, reasonable goals might be:
  • Year 1 - 6 pounds
  • Year 2 - 3 pounds
  • Year 3 - 1.5 pounds
  • Year 4 - 0.75 pounds
  • Year 5 - 0.375 pound

Other Natural Muscle Building Potential Standards

We have established that Dr. Casey Butt's standards are backed by extensive research. In my opinion, they are the gold standard. But how do these standards compare to the opinions of other prominent industry experts? Let's take a look.

Natural Bodybuilder

Lyle McDonald on Natural Muscle Building Potential

I'd note that while I do believe trainees should simply get into proper training and not worry up front what they may or may not accomplish, I also believe that there are genetic limits set by underlying biology (again, modulated by behavioral choices and patterns). That's just reality and recognizing them can save people from a lot of mental anguish about what they think they should be able to or could be able to accomplish if they just worked hard enough.

  • Year 1 - 2 pounds per month, or 20 to 25 pounds the first year.
  • Year 2 - 1 pound per month, or 10 to 12 pounds the second year.
  • Year 3 - 0.5 pounds per month, or 5 to 6 pounds the third year.
  • Year 4 - 2 to 3 pounds the third year.
Here we see the same rate of decrease: 50% from year to year. Lyle McDonald nailed it. Do I believe that a natural lifter can gain 20 to 25 pounds of muscle mass during his first year of training? No. This rate is far too generous, even when diet and training are absolutely perfect and the lifter is a natural freak.

Lyle's calculations allow a lifter to gain 50 pounds of muscle over the course of his life. The only scenario in which this is possible is if the lifter is starting out underweight. Let's look at an example.

Here our subject is 5'10", 160 pounds, and 15% bodyfat. This would put him at a lean body mass of 136 pounds, while carrying around 24 pounds of fat. These are rather normal, average numbers for a teen.

Using these base numbers, let's see how Dr. Casey Butt's predictions stand up to Lyle McDonald's guidelines. Assuming for the sake of simplicity that out lifter adds no fat during this process (far-fetched, but makes the math easier):
  • Dr. Casey Butt - Lifetime 35 pound natural muscle mass gain. 171 lean body mass, 24 pounds of fat. Total weight of 195.
  • Lyle McDonald - Lifetime 50 pound natural muscle mass gain. 186 lean body mass, 24 pounds of fat. Total weight of 210.
Most current top level natural pros compete at a weight in the 180s. Of course, this weight varies depending on height, but it presents a reasonable comparison point.

With the understanding that competitive bodybuilders lose some muscle mass while trying to lean down for competition, let's take a deeper look at Butt and McDonald's numbers compared to this bodybuilder.
  • Natural Pro Competitor. 5'10", 185 pounds at 6% body fat. 174 pounds lean body mass. 11 pounds of fat. Reasonable off-season stats of 180 lean body mass at around 15% body fat.
This puts our lifter somewhere in between the standards of Lyle McDonald and Dr. Casey Butt. My final thoughts? McDonald's standards are simply too high. Dr. Butt's standards are more reasonable for the average lifter.

Our example lifter is unlikely to be a pro-level competitor, so a 35 pound gain is much more likely than a 50 pound muscle gain.

Marc Perry's Natural Potential Formula

I came up with this short hand approach to calculate your maximum Lean Body Mass (LBM). Your LBM is everything in your body besides fat, including your bones, organs, muscle, and blood.

Marc Perry's formula is:

(Height in Inches - 70) x 5 + 160 = Maximum Lean Body Mass

Based on height, your lean body mass potential shakes out to be:
  • 5'4" - 130 pounds
  • 5'5" - 135 pounds
  • 5'6" - 140 pounds
  • 5'7" - 145 pounds
  • 5'8" - 150 pounds
  • 5'9" - 155 pounds
  • 5'10" - 160 pounds
  • 5'11" - 165 pounds
  • 6'0" - 170 pounds
  • 6'1" - 175 pounds
  • 6'2" - 180 pounds
While this is a reasonable goal for the non-muscle head who is not after a maximum amount of muscle mass, it is far from a "maximum potential." In my opinion it is about 15 to 20 pounds low.

Martin Berkham/Lean Gains Natural Potential Formula

Suffice to say, the bodybuilders that appear on the cover of muscle magazines serves as poor role models for what's possible without "assistance". Establishing reasonable goals and limits for natural bodybuilders and athletes is important in order to put things into context. A ripped 170-180 lbs is often scoffed at in some circles. You're not "big" until you're 210-220 lbs (or so the talk goes). What these people don't realize is that ripped 170-180 lbs would look very impressive on a guy of average height. In fact, few natural guys will ever achieve those stats due to the consistency in training that it requires.

Here is the formula:

(Height in centimeters - 100) = Max Body Weight in Kg When @ 5-6% Body Fat

Let's look at max weight at 5 to 6% bodyfat, and lean body mass potential:
  • 5'5" - 143 pounds max weight, 135 pounds max lean body mass
  • 5'6" - 149 pounds max weight, 140 pounds max lean body mass
  • 5'7" - 154 pounds max weight, 145 pounds max lean body mass
  • 5'8" - 160 pounds max weight, 150 pounds max lean body mass
  • 5'9" - 166 pounds max weight, 156 pounds max lean body mass
  • 5'10" - 171 pounds max weight, 161 pounds max lean body mass
  • 5'11" - 177 pounds max weight, 166 pounds max lean body mass
  • 6'0" - 182 pounds max weight, 171 pounds max lean body mass
  • 6'1" - 188 pounds max weight, 177 pounds max lean body mass
  • 6'2" - 194 pounds max weight, 182 pounds max lean body mass
As with Marc Perry's model, Berkham's formula lands on the light side. While this physique would look amazing at 5 to 6% bodyfat, it's about 15 pounds light at that degree of leanness.

Final Thoughts on Natural Potential

When analyzing all the methods and formulas of determining how big a lifter can get naturally, we find that many formulas land on the light side while Lyle McDonald's formula is quite generous. Dr. Casey Butt's study is more towards the middle of the pack, with a slightly more aggressive potential.

This is good news for naturals. It means that the average male actually has potential to exceed most of the formulas found on the Internet. Its also bad news for naturals, as reality sets in. Every expert is beating the same drum...

There is a limit to how big you can get naturally, and it's no where near the size of Mr. Olympia.

Let's be real here for a moment. A 30 pound muscle gain is a lot of mass. It will dramatically transform your physique, and everyone will know that you lift. It's not exactly "small."

With that said, no one will mistake you for Arnold Schwarzenegger. But, you'll likely have every bro at the gym asking you for your secrets... Or asking you "what you take."

At the end of the day, focusing on potential is a waste of time. It is best to focus on what you can control: Gym effort and a proper eating plan. Combine these two essentials, monitor your measurements, and be patient. It takes 4 to 5 years to build an amazing natural physique.

By that time you will have a good idea of how big you can get naturally. You will also have an understanding of how difficult it is to pack on muscle mass after the first several years of training.

Natural Arm Size Guidelines

Now that we have established reasonable natural potential, let's talk arm size. If you still believe that 20 inch lean arms are possible as a natural, I ca not help you. Move along and keep walking right back into fairy tale land.

On the other hand, if you want some quality guidelines for a physique under 15% bodyfat, here goes.

Measure your wrist circumference in inches immediately above the styloid process, meaning on the hand side. To this circumference the following number of inches based upon your current bodyfat percentage.

This presents a reasonable, but hefty, natural arm size goal. It will be a challenge to reach this level, but still represents a good goal.
  • 15% and under - Circumference + 10 inches
  • 16 to 20% - Circumference + 10.5 inches
  • 21 to 25% - Circumference + 11 inches
  • 26 to 30% - Circumference + 11.5 inches
  • 31 to 35% - Circumference + 12 inches
  • 36 to 40% - Circumference + 12.5 inches
  • 41% and over - Circumference + 13 inches
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