I got this awhile back on a quilt site, but don't remember which site, but here's what I have: On-Point Settings
Setting quilts on point requires the addition of "setting triangles" on the sides and corners. To ensure that the straight grain of the fabric is on the outer edges of the quilt, cut quarter square side setting triangles and half square corner setting triangles. (Triangle Tips) Rows are assembled diagonally, starting at the corner. Corner setting triangles are added after rows have been sewn together. TIP: Spray bias edges lightly with fabric sizing (not starch) to help prevent them from stretching.
Setting Triangles - Measurements Include Seam Allowance
Need help cutting setting triangles? Link to "Triangle Tips" page.
No Sashing
10" (finished size) Block
12" (finished size) Block
Corner Triangles
8" Half Square
9 3/8" Half Square
Side Triangles
15 3/8" Quarter Square
18 1/4" Quarter Square
1" Sashing (finished size)
10" (finished size) Block
12" (finished size) Block
Corner Triangles
8 5/8" Half Square
10" Half Square
Side Triangles
16 3/4" Quarter Square
19 5/8" Quarter Square
NOTE: Use the following formulas for calculating setting triangle measurements for other size blocks. Round measurements to the nearest 1/8 inch. Remember to add finished sashing measurement to block size when figuring size for setting triangles on a sashed quilt.
Corner Setting Triangles (Half Square):
... Finished size of block (e.g. 15") ÷ 1.414 + .875 = SIZE
Side Setting Triangles (Quarter Square):
... Finished size of block (e.g. 15") x 1.414 + 1.25 = SIZE
When setting quilts on point remember to use the diagonal measurement to determine how many blocks you will need for the quilt. If you are using a 10" block the measurement would be 14 1/8" (10 x 1.414) Example: Four blocks across and five down measures 56 1/2" x 70 5/8" before the borders are added.
If you blocks aren't these sizes, PM me and I'll email you a more diversified chart, it doesn't come out right on the response. Hope this helps.