Isn't there math involved like adding 7/8" to the setting triangles?? I always oversize my setting triangles because there is NOTHING worse then cutting them just a tad bit too small. I use this ruler for cutting mine:
http://littlefoot.net/product/the-setting-triangle/
Depending on your design, you do need to included the sashing width in your calculations. It sometimes help if you can post a photo of the quilt in progress.