If a yard is 36 inches and the cheer bows you are making are 3 inches wide;
36 (inches) divided by 3 (inches) = 12 Strips
So I would say that you should (in theory) get 12, 3 inch x 30 inch strips out of 1 yard of Spandex. However, It would depend on what way you cut the fabric as although the length you are purchasing would be 36 inches (1 Yard), the width of the actual fabric is usually anything between 44 and 54 inches wide.
I hope that helps