When I buy fabric I always add 1/4 yard to what is needed. I do wash first. When I make the quilt I try to figure the top of the mattress plus at least one block per side for the drop. Then I test the size on a bed to see how it fits with the drop. Then I add borders based on the "look" from the bed test. I do not measure the size other than that. I do square up blocks to size but that is it. I always figure for some shrinkage and do wash after quilting but will only do a bed check after the quilt is finished just to see how it looks. I am not a big fan of heavy quilting so do not expect a lot of shrinkage from the quilting.