I add up the width and length twice and add 20. Then divide by 40 to get number of strips needed. You do need a little extra for the corners plus fudge factor. So for a 50X70 I would get 240 + 20 = 260 divided by 40 = 6.50 and round up to 7 strips. Hope this makes sense. The amount of fabric need would be the size of strip (2 1/2") by number of strips needed plus one. So for 7 strips, I would say (7 +1) = 8 X 2.5 = 20 inches.
Last edited by Rumbols; 12-14-2011 at 10:13 AM.