don't wash it first, it's the shrinking that makes the nice "rag" look when you wash it even fluffier.

These are great instructions that you can print out, it's what I used to make my first rag quilt. Go down to the bottom of the page and click "Let's Make A Rag Quilt" for their instructions.

http://www.lovetosew.com/ragquilt.htm

The only thing I do differently now is I make my center square 2" smaller than my outer square. So if I have an 8" square, I make the center 6", that way I get the same warmth as 3 pieces of fabric but I only have to trim 2 pieces of fabric for edges. And I use flannel in the middle instead of batting.

I never prewash for the rag quilts

I pre-wash everything...some fabric shrinks or bleeds. We no longer have a laundromat, so I vacuumed mine, washed in the top-loader (checking the lint catcher often) and line dried flat over my parallel line dryer. Ragged nicely without going in the dryer.

The quilt will be nicer if you wash it after it is finished. The shrinking will add to the 'thick' feeling. It will also make the rag edges fray better if you wait.

I agree with pre-shrink atleast one time. I always use a "colorcatcher". Bad experience, even after I pre-washed all the fabrics for a quilt for daughter. So please don't take any chances.
Pre-shrink on the advice of an Extension agent and Home teacher and just plain sewing/quilting experience. ***Always pre-shrink/prewash and always when making Rag quilts, use the laundramat to "rag out". It's too hard on your machines. And the laundramat machines, the heavy duty ones are more industrial for this type of step in quilting. I've also used the laundramat for the doing the Faux chenille scarfs that are made of flannel.

When making a rag quilt with flannel, you do not wash the flannel first. Only wash it after you have finished making it, and put it in the dryer with a towel to help with the ragging process. Your rag quilt will turn out nice this way.

WASH IT FIRST!!!!!

Let me tell you of the experience I just had last month.
I made a raggy quilt for my soon to be two grandbaby. I did not wash the flannel first. It was crib size. I washed it twice when it was done and when I got it out of the dryer it was way less then crib size. Well what to do now??? I bought a doll and sent the raggy quilt with it as a doll blanket. My son asked why I would make such a nice doll blanket, it should have been a litte bigger so baby could use it!!! UGH!!! I am now making 8 raggy quilts for my grandchildren for Christmas, I washed and dried ALL the fabric!!

I have made dozens of rag baby quilts out of flannel and have never had a problem with shrinking. I have never washed the material before making the quilt, only afterward. Also, one of the clues that I like best is to put a terry cloth towel in the washing and drying cycle. It helps a lot in the "fraying" process. I also wash the baby quilt and the towel alone in a full water cycle. It seems to swish around more which makes a beautiful ruffle. But, like one of the posts says, a dozen quilters, a dozen answers. LOL

I usually wash flannel before because of the shrinkage but when makomg a rag quilt don't. It will rag much quicker without prewashing. Be sure to check your thingy (can't think of what it is called) on your dryer that catches lint several times because there will be alot and could be a potential fire hazard. I have taught this class a number of times and always give these instructions. Please post a picture when done. Winter is coming (hard to beleive) and my rag quilt is my favorite for keeping warm. I purposely made it under 72" so my husband (6'4") wouldn't steal it from me. (Evil laugh)/

It looks to me like it is 6's. If you don't want to wash first, make the quilt a little bit bigger just in case it shrinks. If you want to wash first to pre-shrink, go for it.