How to Make Setting Triangles
 Time to get the Calculator! This involves some Formulas! I'll show you how to do the math, and include some pre-calculated sizes below!
 CORNER SETTING TRIANGLES:  Finished block size divided by 1.414, plus .875  for seams, rounded up to the nearest 1/8" Make SQUARE this size and cut it in half once on the diagonal to make two corner half square triangles. SIDE SETTING TRIANGLES:  Finished block size multiplied by 1.414, plus 1.25 for seams, rounded up to the nearest 1/8" Make SQUARE this size and cut in half twice on the diagonal to make four side quarter square triangles.
 EXAMPLE: To accompany a finished 12" block, for the corner triangles... 12 / 1.414 = 8.489 + .875 = 9.364  or 9-3/8" square, cut in half once diagonally and for the side triangles... 12 x 1.414 = 16.968 + 1.25 = 18.218 or 18-1/4" square, cut in half twice diagonally

 Common Setting Triangle Sizes Finished Block Size Side Triangles Corner Triangles 4" 7" 3-3/4" 5" 8-3/8" 4-1/2" 6" 9-3/4" 5-1/8" 7" 11-1/4" 5-7/8" 8" 12-5/8" 6-5/8" 9" 14" 7-1/4" 10" 15-1/2" 8" 12" 18-1/4" 9-3/8" 14" 21-1/8" 10-7/8" 15" 22-1/2" 11-1/2" 16" 23-7/8" 12-1/4"
 Oct 2002 Marcia Hohn