I do measure before and after -- I can't seem to find the paper where I have written this down at the moment :). I measured a quilt - no borders - that started out 60" x 60" and it shrunk to 54" x 54" - Fabric preshrunk, Warm & Natural 100% cotton batting, quilting not very dense.
I allow at least 6 inches both ways. If I have a border, I will make the border a bit wider to cut back after quilting, not that it helps in the shrinkage from washing.
Go measure one of your quilts that you have washed and dried.
Measure the individual blocks that you know what the measurement was before you washed the quilt. Compare that with what it is now. Consider the type batting you used.
My DH likes a certain size for his Watch TV/Nap in the recliner
quilt -- he doesn't want it too big. He sees the process and still wants only that exact size ~LOL~.
If I find that piece of paper over the weekend, I'll post again.

I'm not a fan of the puckered look, especially since I do scrappy quilts and (to me) a few really puckered pieces out of several hundred smoother pieces just looks weird.

Check the batting manufacturer's notes. They will usually mention potential shrinkage along with their recommendation for quilting. If that info is not on the bag or wrapping tissue, check for a company website... those often have more detailed info than on the wrapping.

I don't use cotton or wool batting. I don't like the weight or the often finicky laundry requirements; and I detest seeing a quilt sewn to 90"x90" shrink down to less than 80x80 -- it's happened and that wasn't a pleasant experience.

I use polyfill batting, do prewash all fabrics and, in spite of that, I have had quilts shrink as much as 3 inches - one that shrank 9 inches in both directions. That's noticeable even in King-size. I get around the shrinkage issue a bit by doing a border 2" wider than needed, turn under and baste the quilt's raw edges closed, then machine wash and dry. Then I measure again, trim excess border and bind.

I do add about an inch for high-loft, and 2 inches for extra-high loft, but I think there's a lot of flexibility. And -truthfully- I doubt anyone other than an experienced quilter who already knew what you were aiming for, would ever notice the difference. Unless your DD is a professional decorator or upholsterer (or persickety enough to use her tape measure), she will not notice an inch's difference in size.

Interesting discussion I'd never considered. The quilts I give away have generally been lap quilts of varying sizes, or wall quilts.

Haven't completed the quilting on any of my bed size, now I'm thinking I'd better think hard about fit. What I thought was bed size may become a coverlet.

Yet another reason to love this forum. Thank you all for the ongoing lessons.

LindaB/CA

Thanks for your input, Marsha and Meldy. Like Linda, most of my quilts have been lap quilts, so I never worried about size. I'm making it two inches longer and three inches wider. That's the most I can increase it with the fabric I have. I hope it suffices.

Lois, if you use a cotton /poly batting, your quilt will shrink much less. I like Warm Blend, which is a 50/50. I have a hard time telling the difference on the roll from the Warm & White. I like how it quilts, again almost no difference. Also wash the completed quilt (with the binding attached) in a cooler water, dry on a low/ med setting, remove when still damp and block it.
It will be less crinkly, obviously from less shrinkage. :~)
Less crinkly is a good look for modern quilts in my opinion.
If you have a JoAnn's near you, use a coupon to buy it - it is more expensive than the Warm & Natural.

Here is a link that might be useful: Warm Blend