How Many Moves Deep into Opening Variations Do You Study?

Say you're studying the Sicialian Najdorf and use a particular variation of it.  How many moves deep do you study typically on average?  ...10, 15, 20, 20+?

20? Christ man. I think the Ruy Lopez is the only one I've gone more than 5 deep on. 

Haha! Actually, common openings such as the Ruy Lopez and the Sicilian Defense are analyzed well beyond move 20!

In my case, 7-9, just so I know the defining moves of the Sicilian and where to go from there.

It varies by individual line.  Some lines I know only 8 or 9 moves in, some I know 25.  I try to end my lines when it is clearly a middle game and the position is quiet.  The line I use for opening/middlegame is: "are all of the pieces developed and the rooks connected?

I typically play four or five moves than move into my own non-award winning variation.

As Black I play the Caro-Kann and the Slav defense. In the Caro-Kann the deepest line I know is 15 moves, although I have an idea of the middle game plans. Most lines I might know to about 10 moves. It's probably the same with the Slav.

As White I play the English and probably don't know any lines more than 10 moves deep, but know quite a few opening plans and ideas.

You should know enough lines not to get into trouble (how many depends a lot on your level), but generally people don't need to know much theory. They key is to learn middle game plans and ideas.

As for me quite a lot because I also want to understand the arising middlegames well

What about variation lines?  Do you study (or memorize) these, too?  I have found that there are way too many and end up trying to play sound chess principles.

Playing at a 1057 rating my opinion is the Najdorf is well beyond your level. I would suggest learning something much less theoretical. It isn't only memorizing the moves but more importantly understanding the reason behind the moves

I take a look at pretty much every sensible move/idea, but try to memorize only the main lines.

I agree.  Maybe learn the first three moves as to not have a quick mate and then play your own personal line.  You will find by trial and error what works

memorising opening lines and reproducing them in games requires no chess ability

If a move both strikes me as strong and surprises me then I will look it up after the game.

There are lines that will blow my Najdorf out of the water but my level opponent normally dont know them deeper than I do.

Not very deep. I know a few lines to move 12ish but not many. I tend to know 4-5 moves deep in the lines I play. I do have a decent amount of expierenced in the kings gambit simply because I have OTB and online around 4-500 games in it

I usually know about 5.

I made it to USCF A class without any serious opening study.  

Normally 10 to 12 moves in single variation...And watching 2-3 games of that variation...And in one opening i prepare 5 -6  main variation and single variation include 4-5 sub variation...

Yeah I'm the opposite. My improvements come when I fix a technique issue. Recently I had a huge improvement when I started practicing being more patient with positions and not blindly attacking

I completely agree with you BettorOffSingle.

I find alot of players who get into a position they are familar with even if they only have memorized the first 5 moves they often feel alot more confidence in their game.

Confidence and comfort are really huge in chess that is for sure.