# calculating yardage bench cushions?

I have four slabs of foam about 3" thick,  each: L 32 5/8" X W 14 5/8"  I plan to sew  box-type cushion slip-covers for each.

How much yardage should I buy? I figure I should add about an extra yard for errors?

Any advice in this regard would be greatly appreciated.

blessings

I think the first thing is to figure out what exact pieces you will need for construction.  Assuming you use a 5/8" seam allowance, you'll need the following pieces for one very basic cushion slipcover:

-One 4 1/4"  x 33 7/8" (Front length)
-Two 3" x 33 7/8" (Back opening)
-Two 4 1/4" x 15 7/8" (Sides)
-Two 15 7/8" x 33 7/8" (Top and Bottom)

You will have a lot of "extra" fabric regardless of whether you use 45" or 60" or somewhere in between because you will still want to keep with the grainline which will also retain any direction the fabric pattern might have.  A 45" fabric will leave the least "wasted" fabric.  If you cut absolutely perfectly, you will need 46 1/4" or  ~1.28 yds, but you'll probably want 1.5 yds for cutting.  I hope this all makes sense.

Here's an image (to scale) of what to expect with the fabric open: