One thing's for sure: A 19 inch neck is well above the average neck measurement—even for those who train their necks directly.
The real question should be this: Is having a 19" neck good or bad?
I'll be answering this question from both a health and an aesthetic standpoint so that you can learn the pros and cons of having a 19 in neck.
How Does Your Neck Compare?
Is a 19 inch neck big?
A 19 inch neck is definitely big, regardless of whether you have a lean 19 inch neck or a fat 19" neck. Indeed, such a neck size is around 4 inches bigger than average for a man, meaning that a 19 inch neck is pretty huge.
Most people simply don't have the genetics to develop a muscular 19 in neck. Of course, if you weigh over 300 lbs and train your neck directly, then you might well be able to sculpt a 19" neck. But for the rest of us, building a natural 19 inch neck that actually looks lean is virtually impossible.
On the other hand, if you bulk up to a high body weight and gain some fat along the way, then it's definitely conceivable that you could end up with a 19" neck. The issue is that you'd lose a lot of definition while potentially sacrificing your health.
After all, research shows that neck size correlates with sleep apnea, but not as strongly as being obese does.  So when you increase your neck circumference and gain a lot of body weight, it does seem like you're increasing your risk of getting sleep apnea, which is no laughing matter.
How large is a 19.5 inch neck?
A 19.5 inch neck is very large indeed. If you have a genuine 19.5 inch neck without having excess body fat, then it's likely either because you trained your neck directly for a long time or because you simply have the genetics to be able to build a thick neck.
Of course, having a 19.5" neck may be undesirable if it's out of proportion with the rest of your physique (and it could certainly make buying clothes a nightmare). And that's without the potential health consequences that come with having a neck that thick.
Sure, having a 19.5 inch neck might help to protect against concussion—which is useful if you play contact sports. But you don't need a 19 inch neck to get the concussion-prevention benefits of having a strong neck.
After all, most athletes don't have 19" necks. And besides, having a thick neck is no guarantee of avoiding injury. So, by all means, train your neck, but don't feel like you need to build a 19" neck for any reason.
What shirt size is a 19 inch neck equal to?
In most clothing brands, a 19 inch neck is equal to a size 3 XL (that's 3X large). Just note that if you have a 19" neck circumference, you'll actually want to select a collar size a bit larger than 19 inches so that you have some breathing room.
In some cases, a 19 in neck might be equal to a 4 XL. But based on my research, a 19 or 19.5 inch neck usually works out at a 3 XL.
Now, if you have a neck that's genetically much larger than the rest of your body (relatively speaking), then it might be hard to find off-the-peg shirts that fit you well. If this is the case, then you'd need custom-fit clothes so that the shirt isn't too tight around your neck or hanging off the rest of your body.
19 inch neck case studies
Here are 3 men who have thick 19 inch necks. Learn how they built such huge necks and see what a real 19 inch neck actually looks like.
Alex from AlphaDestiny built a flexed 19 inch neck and said that the neck is one of the fastest-growing body parts. This is good news if you're insecure about having a skinny neck because, in a matter of months, you can have a substantially thicker neck if you're consistent with your training.
Just make sure to focus on progressive overload (you know, like you would with any other body part) once you nail the form. So many people erroneously go light on neck training (and forearm and calf training, for that matter) and then wonder why their circumference measurement is exactly the same.
I'm not saying that you should do low rep neck curls and extensions. After all, high reps give your neck muscles way more growth-stimulating training volume, and they protect against injuries. Still, you should aim to increase the amount of weight that you can neck curl and neck extend for sets of 30 reps.
Alex from AlphaDestiny is especially good when it comes to insanely high rep neck training. So I definitely recommend checking out his extensive library of neck training tips if you're serious about taking your neck size and strength to the next level.
Phil Gervais of PG Coaching and StatueFit took his neck from a skinny 14 inches to a colossal 19 inches. He's a big proponent of high-volume training, and I've seen him recommend 5 sets of 20 reps for neck flexions and extensions.
By doing sets of 20 reps, you'll naturally minimize the side effects that come with neck training and greatly reduce your injury risk. At the same time, you'll also be giving the fast-growing sternocleidomastoid muscle the volume that it craves.
You can see in various videos that Phil uses a neck harness as well as manual resistance (putting the plates on his head). Both options work, and I recommend giving each of them a try to see which one feels the most comfortable.
Comfort is an underrated aspect of neck training because when you're comfortable, you can train harder and establish a stronger mind-muscle connection with your neck.
The man behind the YouTube channel BrawnMediaOfficial has a verified 19 inch neck (he measured it on camera with a tape measure). Although he doesn't have much published information on neck training, it's obvious that he's a big fella who lifts very heavy indeed.
I don't know whether he trained his neck directly to get it to 19 inches, but he certainly looks like the strongman type, and strongman competitors definitely have big necks (you can't not have a thick neck when you weigh 300+ pounds!).
Is having a 19" neck bad for your health?
From an aesthetic standpoint, having a 19 inch neck can definitely make your physique look a lot more powerful—intimidating, even.
But is all that neck mass bad for your health? It seems that way. Although numerous people have built a 19" neck without suffering any health consequences, having such a thick neck could certainly increase your risk of sleep apnea.
This is especially true if your 19 in neck is accompanied by obesity, large tonsils, and other sleep apnea risk factors. 
So if you're concerned about your health, then it might be a good idea to avoid making your neck so big. After all, you don't need to have a 19" neck to have a muscular neck!
The verdict on having a 19 in neck
It takes a lot of time to build a lean 19 inch neck, and some lifters just don't have the genetics to get a neck that thick. Still, if you hang around at a higher body fat level (let's say around 20%), then it's conceivable that you could build a 19" neck over a number of years.
Of course, a big question that you need to ask yourself is this: Is it worth it to actually build a 19 in neck?
If you want to enjoy optimal health, then I'd say no. As you saw with the above case studies, it's possible to have a 19 inch neck while living in good health, but why risk it?
You can look big and muscular while having a neck that's significantly smaller than 19 inches.
- Pływaczewski, R., Bieleń, P., Bednarek, M., Jonczak, L., Górecka, D., & Sliwiński, P. (2008). Wpływ obwodu szyi i wskaźnika masy ciała na zaawansowanie obturacyjnego bexdechu sennego u mezczyzn [Influence of neck circumference and body mass index on obstructive sleep apnoea severity in males]. Pneumonologia i alergologia polska, 76(5), 313–320.
- Benisek, A. (2007, January 1). Sleep Apnea. WebMD. https://www.webmd.com/sleep-disorders/sleep-apnea/sleep-apnea