You want to make sure that the body is tapered down to the hip; that will prevent the extra muffin-top fabric that spills outside of your waistband when you try to tuck in your shirt, like the guy in this photo.

Your dress shirt will be longer than your sport shirts, since dress shirts are meant to be tucked in, while sport shirts are designed so you can wear them untucked. We covered the differences more thoroughly in this Back to Basics article, so feel free to check that out.

Neck

The best way to measure your neck is with tailor’s tape.

The second best way is to guesstimate, and then take a few shirts with you into the fitting room and try them on.

Rule of thumb: You want one to two fingers’ worth of space between your shirt collar and your neck. –

Here’s what I mean. Simply place your middle finger on top of your index finger (like you’re about to cross your fingers, but you didn’t go all the way), and with your shirt buttoned all the way up (yes, even your collar), see if you can fit that finger stack between your neck and shirt collar.

For some guys, one finger will work just fine. You have to see what you’re comfortable with.

Can’t fit your finger or finger stack in there? Your shirt collar is too tight. Go with 1/2 size larger, and keep sizing up until you can get your finger in there. If you can button your collar but can’t fit a finger, you most likely will only have to go 1/2 size up.

On the opposite end, can you fit your whole fist in there? Your shirt is too big, my friend. Size down until you find the sweet spot.

Sleeve width

If you’re picking up a more modern dress shirt (stores can use “modern”, “tailored”, and “slim” interchangeably), you shouldn’t have to worry too much about shirt sleeve width. Since the rest of the shirt is trim, your sleeves will be as well.

Watch out for shirts with a lot of extra fabric in the sleeves; you don’t want a shirt like that.

Side Note: For you more hefty gents carrying a bit more girth (whether that’s fat or muscle), don’t immediately dismiss modern- or slim-fit dress shirts as only for skinny dudes. Find your size and try one on; I bet you’ll be pleasantly surprised.

Source: effortlessgent.com