Measuring fabric before and after washing it
I am definitely in the "if it's washable, wash it before cutting it" group. I want to wash the thread, too, but that has not seemed feasible!
Anyway, I have measured hundreds of pieces of fabric before and after washing. I was wondering if there actually was shrinkage - because a couple of pieces of cat print fabric were about 37 inches at the time I bought them - and were only 35 inches long when I wanted to sell them!
What I have found:
Most of the cotton woven fabrics shrink
Usually the shrinkage is in only one direction - I am unable to predict ahead of time which direction it will be
Brand name does not seem to matter - I have had shrinkage (and bleeding) from every line - including ones that I had "assumed" would be "better"
I have had shrinkage up to 2.5 inches in width on a 42 inch Michael Miller black (from three or four different bolts)
Even a Roc-Lon "pre-shrunk" muslin shrunk about two inches in length per yard when I washed it! That did surprise me.
It matters enough to me to bother with the soaking in hot water, then washing gently and drying "until done" before cutting the fabric.