Are 13 inch biceps big or small for a natural lifter? You'll soon find out!
It seems like every lifter is obsessed with the size of their biceps brachii. But like most things in fitness, there's no one size fits all approach.
Whether 13 inch arms are big or not depends on important factors like your height and body fat level.
As you can see on the biceps size chart below, having an unflexed 13 inch arm circumference is actually completely normal. For the remainder of this article, however, we're going to be talking about flexed 13" arms.
How Do Your Arms Stack Up?
Are 13 inch arms big?
Are 13 inch arms big and muscular? Here's what the data has to say.
Based on research from the Centers for Disease Control and Prevention, 13 inch arms aren't big— they're an average size. 
The catch is that these measurements were, in all likelihood, taken unflexed. How do I know that?
Well, I'm not 100% certain. But since they took arm measurements for kids as well, I highly doubt that they'd ask toddlers to flex their biceps. So for the sake of consistency, the researchers probably took unflexed circumference measurements.
Most people have bigger arms when they flex, so if your biceps are only 13 inches flexed, then they're likely below average in terms of muscularity, especially if you have a high body fat level.
On the other hand, if you're fairly short (let's say 5'7" and under), and you have good arm definition, then 13" biceps can actually look pretty well-developed.
This is especially true if you're a short, shredded bodybuilder (who would presumably have much bigger biceps if they didn't have such a dearth of body fat).
Are 13.5 inch arms big?
Are 13.5 inch biceps a good size for a natural lifter?
It depends on your age, height, weight, body fat, training experience, and measurement state.
If you're fairly tall (let's say 5'10" and over), have a high body fat level, have been training for years, measured your arms with a pump, and they're still only 13.5 inches, then no, they're not big.
Conversely, if you have a year of lifting under your belt and lean 5'5" physique, then yes, 13.5 inch arms are actually quite impressive, presuming that you measured them cold.
13 inch bicep case studies
These 13 inch bicep case studies show you what 13 inch arms flexed look like at various heights and builds.
Case study 1: Fitness nitu
The man who operates the YouTube channel Fitness nitu is 5'7" (170 cm) and has 13 inch biceps (roughly 33 cm biceps).
While his arms don't look massive, his biceps and triceps evidently have excellent muscle definition, something which is confirmed in his other flexing videos.
If he had a normal amount of body fat, he'd get 34 cm biceps and 35 cm biceps in no time at all.
In other words, this guy has a great foundation of lean mass and good muscle insertions. If he stays consistent and increases his body weight, then I don't think it will be long before he reaches the 14 and 15-inch club.
Case study 2: Rahul Singh
Rahul Singh is 5'10" and has 13.5 inch biceps (the video above shows him with 13 inch arms, so he's clearly making gains).
The first thing that's obvious is that his entire physique is very lean, which may be because he competes in MMA.
Of course, his arms don't look like those of a bodybuilder, but he's got the foundation to build a very muscular pair of arms if he keeps lifting.
He's also an excellent case study of how you can go from 13 inch to 13.5 inch arms in a relatively short space of time while maintaining a low body fat level.
Case study 3: Troy Adashun
Troy Adashun is 6'1" and made an excellent video explaining how he went from having 13 in arms to having 18-inch pythons in around 7 years.
Now, at a glance, his previous arm size looks a lot bigger than 13 inches, but it could just be the lighting and angle (which can make your arms look a lot bigger than they actually are).
Anyway, he gave some excellent arm-building advice in his video. So if you want to exceed 13" arms as a natural lifter, then I definitely recommend watching his video in full.
He stresses the importance of eating enough calories to bulk up your biceps and triceps. After all, if your body weight isn't increasing, then it's unlikely that you'll transform your arms.
But what was really interesting is that he shows you just how easy and simple it is to consume enough quality calories. Far too many lifters have excuses as to why they can't get weight, but after watching Troy's video, you'll see that your "reasons" for not eating enough are really just weak excuses.
Troy also makes it clear that you need to combine different training styles and intensity techniques if you want to grow your arms.
Not only do you need to perform heavy curls and extensions for sets of 8-10 reps (mechanical tension), but you also need to lift lighter weights for higher reps (metabolic stress) and do slow-negatives to break down the maximum number of muscle fibers (muscle damage).
13 inch bicep FAQ
If you want to know whether or not having 13 inch biceps flexed is impressive for your particular age and height, make sure to read this informative FAQ section for the answer.
Are 13 in biceps good at 5'7"?
Are 13 in biceps good at a height of 5'7"?
While I'd love to give you a simple yes or no answer, the reality is that it depends primarily on your body fat level and training experience.
If you have a lean physique and are able to see arm veins and muscle separation, then 13 in arms can actually look quite big and impressive (but likely not massive). This is especially true if you've only been training for a couple of years or less.
On the other hand, if your body fat percentage is over 20% and you've been lifting for 5 years already, then 13" arms aren't that impressive and are actually smaller than average.
Are 13" biceps good if I'm 6 feet tall?
If you're 6 feet tall, then you're definitely above average in terms of height.
However, you're definitely below average in the arm size department if you're 6 feet tall and only have 13 inch biceps.
This is because taller lifters such as you and I have longer bones and muscle bellies. Therefore, we also have the capacity to build bigger muscles overall (in terms of circumference measurement).
So if your arms only measure 13 inches, then they're very far away from their genetic potential, which is why they won't look very "filled out."
On the other hand, having 13 or 13.5 inch biceps will look better if you're short because your arms will, by definition, be closer to their genetic potential and thus look more filled out.
How impressive are 13 inch biceps for a teenager?
The above chart will give you some indication of how normal your biceps are.
For example, if you're 13 years old, then 13 inch biceps are well above average.
It's the same story if you or your child is 14 years old; 13" biceps are bigger than average.
Even if you're considerably older, let's say 16 years old—a typical age to start working out—then at 13 inches, your biceps are still above average.
That said, the measurements that you can see in the chart are unflexed measurements. However, most people who exercise and lift weights tend to measure their biceps in a flexed state so that their biceps can show their full muscularity.
How can you go from 13 to 13.5 inch biceps?
Going from 13 to 13.5 inch arms comes down to eating enough calories, training your arms directly but not excessively, and getting good recovery (enough sleep, sufficient time between workouts, etc.)
Of course, if you have 13 in arms cold, then you could just do a workout and temporarily get 13.5 inch biceps by measuring them with a post-workout pump.
However, if you want to gain half an inch of pure muscle, then you should follow the above advice while exercising your patience.
Real muscle growth doesn't happen overnight. It will take months for your biceps to go from 13 inches to 13 and a half inches (2-3 months is realistic if you're bulking and still have plenty of arm mass left to gain).
The verdict: Are 13 inch biceps big or not?
Are 13 inch arms big for a natural lifter or not?
In general, no, 13 inch biceps aren't that big for a natural lifter because 13 inches is a normal unflexed bicep size (your flexed measurement should always be bigger than your unflexed measurement).
However, circumstantially, a 13 inch bicep circumference can be big.
If, for example, you're short, have a low body level, and only have 12-18 months of training experience, then 13 inch biceps aren't actually that small.
Of course, with the right lighting and angles, you can also make your arms look a lot bigger than they actually are, which is the essence of bodybuilding.
- Centers for Disease Control and Prevention. (2021, January). Anthropometric Reference Data for Children and Adults: United States, 2015–2018 (National Center for Health Statistics). United States Department of Health and Human Services. https://www.cdc.gov/nchs/data/series/sr_03/sr03-046-508.pdf
- Zeratsky, K. (2020, August 27). Underweight? See how to add pounds healthfully. Mayo Clinic. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/underweight/faq-20058429