A 13 inch neck is very much the average neck size for women but slightly smaller than average for a man. This article discusses the benefits and drawbacks of having a 13" neck and then discusses how you can both build and reduce your 13 in neck.
Compare Your Neck Size:
Is a 13 inch neck big for a woman?
No, a 13 inch neck is not big for a woman; it's a very normal size for a female. Although not an absolute guarantee of good health, having a 13" neck is a fairly reliable indicator that you're not overweight.
Of course, if your neck is slightly smaller or larger than 13 inches, then that's likely nothing to worry about either. Scientists are still trying to figure out how reliable neck size is for determining various health risks.
Some women naturally have genetically skinny or genetically thick necks. There's not much you can do about the latter besides maintaining a healthy body weight and avoiding resistance training exercises that directly work your neck muscles, such as shrugs.
Is a 13 inch neck skinny for a man?
Yes, a 13 inch neck is pretty small and skinny for a man and might even be an indication that you're underweight. Specifically, a 13" neck is about 1-2 inches smaller than average for a male.
According to the data, men typically have bigger and stronger necks than women. 
However, this isn't always the case. For example, if you take a male and a female and the woman lifts weights, but the man doesn't, then it's conceivable that she could actually have a larger neck than him.
Of course, this isn't to say that having a 13 inch neck or a 13.5 inch neck makes a woman look manly because it certainly doesn't. Rather, it just demonstrates that resistance training (especially direct neck training) and body weight increase are two ways to develop your neck muscles.
How can you grow your 13 inch neck?
It's commonly said in the online fitness world that having a skinny neck makes you look, shall we say, a bit goofy and not especially masculine.
On the other hand, having a thick neck typically results in a powerful-looking physique. For this reason, many skinny guys want to bulk up their necks so that they have a more aesthetic physique and greater self-confidence.
For the fastest and best neck gains, you should train your neck directly (which is to say, isolate it) like you would any other body part. Neck curls will build your sternocleidomastoid, whereas neck extensions will build the upper fibers of your upper traps.
Start with 3-5 sets of 20-30 reps per exercise. Do each exercise once a week to begin with so that your newly trained neck muscles have plenty of time to recover. Then, as you get used to the frankly unusual stimulus, you can increase your training frequency to twice per week.
How can you reduce your 13" neck?
Although some people might want to reduce their 13 or 13.5 inch neck, that might not be the best decision for your health. No, this isn't what it sounds like.
Having a skinny neck won't make you sick. Rather, having an at least semi well-developed neck can help to protect against neck injuries, which could occur if you were in a car accident, for example.
Of course, anyone who plays contact sports, such as rugby or football, could also massively benefit from strengthening their neck. 
Still, if your neck is much larger than 13 inches and you want to slim it, shedding your excess body weight is the way to go. As your body mass decreases, your circumference measurements tend to decrease as well, which most definitely includes your neck circumference.
On the other hand, if you have a genetically thick neck, then there's probably little that you can do to reduce its size besides avoiding exercises (such as deadlifts) that place significant amounts of tension on your neck.
In conclusion: Is it bad to have a 13 in neck?
Having a 13 inch neck isn't bad unless it's an indicator that you're underweight. On the other hand, you could make the case that having a slightly larger neck would be beneficial because it'd likely help you to brace better if you were ever in a car accident or received a blow to the head.
Obviously, since the neck is a very visible body part, a number of people are insecure about the way that their neck looks.
The good news, in this regard, is twofold. Most people don't care how your neck looks, and you can definitely grow and shrink your neck (like any other muscle group) using the above advice.
I hope that this article was helpful. Don't worry about your 13" neck!
- Catenaccio, E., Mu, W., Kaplan, A., Fleysher, R., Kim, N., Bachrach, T., Zughaft Sears, M., Jaspan, O., Caccese, J., Kim, M., Wagshul, M., Stewart, W. F., Lipton, R. B., & Lipton, M. L. (2017). Characterization of Neck Strength in Healthy Young Adults. PM&R, 9(9), 884–891. https://doi.org/10.1016/j.pmrj.2017.01.005
- Attwood, M. J., Hudd, L. J. W., Roberts, S. P., Irwin, G., & Stokes, K. A. (2021). Eight Weeks of Self-Resisted Neck Strength Training Improves Neck Strength in Age-Grade Rugby Union Players: A Pilot Randomized Controlled Trial. Sports Health: A Multidisciplinary Approach, 194173812110447. https://doi.org/10.1177/19417381211044736