Each large triangle is three grids high and three grids wide, or 3" grid x 3" grid = 9" finished size. Add 7/8" to the finished size for seam allowances, for a cut size of 9-7/8".
- 20 blocks x 1 triangle per block = 20 triangles
- 20 triangles divided by 2 (the number that can be cut from a 9-7/8" square) = 10 squares required
- 40" width of fabric divided by 9-7/8" = 4.05, or 4 squares per strip
- 10 squares required divided by 4 per strip = 2.5, or 2 strips plus about a half strip, each 9-7/8" wide.
- 9-7/8" x the 3 required cuts (even though one won't be through all of the width) = about 30".
- 30" divided by 36" (one yard) = .83 yard, bump up to 1 yard to allow for shrinkage and provide a bit of excess for squaring up the crosswise grain.
Follow the same procedure for each part of the block, adding together yardages for like-fabrics.
Customize My Quilt Block PatternsYou'll find lots of quilt block patterns on About.com Quilting. They all include fabric and cutting instructions for at least one block, and many include instructions for multiple quilt blocks.
Quilt block patterns put you one step ahead in your yardage calculations, since they always include cut sizes.