I am useless at following patterns so I don't even bother with the sizes. If I see one I like, I do rough calculations such as deciding on my finished size and dividing this up by the number of blocks I want then calculating the size of the smaller pieces which make up each block. The patterns are quite basic too as I think doing this with a complicated pattern would be a nightmare. I also only do a rough calculation on the yardage and buy more if needed. A dangerous game, I know
But I like 'living on the edge'