tudorkeith is right on this one. I dp this all the time, but still there are times when things don't match up right. If you say you need 8 & 2/3 yards, you might want to go for the 10 yards. If everything comes out right the first time, you will not be throwing your money away. Save the left overs in case, down the line, you have a tear in one of the panels on the seat.

I always order extra to do a job and what I don't use I can use at a later date.