For these instructions, we're going to pretend we need one finished panel 50" long x 40" wide. I've purchased 1½ yards of 45" wide fabric, which translates to 54" x 45".
Fold the fabric in half widthwise, selvedges together. So the folded piece now measures 22½" x 54".
Measure and cut 50" in length. You could either measure down 50" from the top or up 4" from the bottom. Place your ruler and cut.
Pick up your cut piece and fold in half lengthwise (22½ x 25).
And, in half again (22½ x 12½). It's almost like you're folding a bed sheet to put it neatly away in your linen closet – in half and then in half again. Be precise about your folds.
Lay your neatly folded fabric piece back down on your cutting surface. As you remember from our game of pretend, the finished width needed is 40". However, we already folded the fabric in half and the fold is still there, so I actually need to measure half that amount, or 20"
Measure 20" over from the original folded edge, mark a straight vertical line, place your ruler and cut.
Unfold it all, and you have a 50" x 40" panel.
Now ... to push your ability to pretend to the next level, let's say the desired finished result is TWO panels 50" x 15".
Follow all the steps above until you get to the final cut. At this point, slice off the fold first. Just slice off a small amount, like ½" to an 1". Then, measure from that cut line 15" over, and make a second slice. Voilá, two pieces 50" x 15",
For more information on cutting, check out: