This particular cushion is designed for a bench with a 12" x 92.5" seat. You can make the bench by following these instructions.
Step 1: Go Get Stuff
3 yards x 60" x 1/2" Foam Sheeting
3 yards of thick polyester batting
3 yards x 60" fabric for cushion
1 spool matching thread
Step 2: Cut the Padding
Next cut the batting into a 92" x 12-1/8" strip.
Stack the foam and then placing the batting on top. Put it atop your bench and site down to see just how darn comfortable that is.
Step 3: Cut the Fabric
(1X) 12-7/8"" x 18"
(1X) 12-7/8"" x 77-1/2"
(1X) 12-7/8"" x 92-1/2"
(2X) 12-7/8"" x 3-1/4"
(2X) 3-1/4" x 92-1/2"
When cutting the fabric, it helps to keep the fabric flat and the scissor low to the cutting surface. Cut with one hand and gently pull aisde the cut piece with the other hand.
Step 4: Sew
Then, with the right side facing inwards, sew one of the thing long strips to the long edge of these pieces of fabric. Repeat on the other edge with the other long strip.
Next, attach each respective side of the longest solid piece of fabric (facing inwards) to one of the two long skinny strips. When you are done, it should form a fabric tube of sorts
Lastly, again with the right side of the fabric facing inwards, attach each small square to each open end, such that all the sides line up correctly. This will close the cushion and form a proper rectangular shape.
Finally, flip the whole thing inside-out through the pocket. The right-side of the fabric will now be facing outwards.
(just look at the pictures below)
Step 5: Stuff
Battle with flattening it out until it looks about right