it really depends on your stitching style...sometimes your 'shrink-up' can be quite a bit, or very uneven depending on the peices and how tight you draw up your threads, lots of variables and never the same results for 2 different people. i would recommend making a smaller practice block, maybe cut a 6" block, applique it, press it and then remeasure...that would give you an idea if you tend to pull it up lots or not much at all. and base you decision on that. personally i always allow 2-3 extra inches that way i have plenty of trimming/squaring room when the block is done. and i can use the strips cut off for other projects.