Use the QFK pattern as a guide. Do you want more than 1 focus fabric or 1 with 3-4 coordinating fabrics. I just calculate how many blocks I need and size of blocks to find yardage.
If you nedd 6 6" blocks of each color, you would need about 1/4 yard as you can cut 6 blocks for each 6 inch strip you cut. I think that would be the best way to calculate yardage. Just be sure to add a little for mistakes. Add for borders and binding of the colors you want.
OK, is this clear as mud. LOL