Figuring shrinkage -
 

I know the formula for shrinkage is:

(Area before - minus area after) divided by area before

However - if one does not know which way a fabric/batting will shrink - in my experience, it usually shrinks more one way than the other -

Let's say that the end of the bolt says "5% shrinkage" - should I just assume that it will shrink 5% in both directions and base my cutting measurements on that?

Say I will need a piece of batting to be 80 x 100 after washing - and 5% shrinkage - should I cut it at least 84 x 105? (If I had 90 inch wide batting, I would probably cut it at width x 105 length)

If it says 5% shrinkage I don't think you should have any expectations at all. It may shrink 10%, or not at all! I would cut enough that there would be no question that it would be enough, maybe 15% bigger than called for.

Is this a trick question? You made me think on this one. Do you see the smoke rising?

I was thinking that the batting is in the quilt so no need to cut it larger than the quilt backing.

Are you saying that you pre-wash batting? Now I see that in your post you are asking about cutting it before you pre-wash it...??

So I would pre-wash the whole piece of batting and then cut to size. Of course, I would over-size even that.

Geesh! I’m no help at all.

Would you please share how you pre-wash batting?

I wash warm & natural batting before using it.

I bought a roll of it - 40 yards x 90 inches wide - a little much to put in my machine all at once.

https://www.quiltingboard.com/main-f...ml#post8328823 - Post #20

Too funny!

Can you tell I wasn't thinking of roll batting? Now I "get" your question.

I'd cut off 110" and wash it. And then figure how much it shrunk up for future reference. If it shrunk up too much, I'd save that piece for another quilt.

Can't help, I would never pre wash batting.

I don't understand the logic behind prewashing batting. Won't the quilting prevent shrinkage? I've never washed batting and it's never been a problem with the finished quilt.

Have you measured before and after?

Different "requirements" for different folks.

The packaging on some battings say that expected shrinkage is such and such - and give instructions for how to wash it before using it - if one so desires.

Some battingx say "do not wash" before quilting.

If it was me I would cut the batting 90 x 100. You can't go wider
than 90" anyway. So if it shrinks a lot and you are short one way
you can always add another washed piece for length.
Are you planning to wash in cold or hot water?
I wash my quilts in cold water and get about 3% shrinkage with W&N.
Might be a bit more in hot water.
Please let us know how it comes out. I haven't done my experiment
yet. But mine will be with Warm and White which shrinks more than
W&N.