Quiltingboard Forums

Let's Cut Corner Triangles
We'll cut two corner triangles by slicing a square once from corner to corner.
Start by calculating the finished length of a block's diagonal.
1. Finished block size x 1.41 = finished diagonal
2. Divide the answer, the finished diagonal, by 2. Add 0.875" and round up to the nearest 1/8" to find your parent block size.
3. Cut two parent blocks that size and divide each in half once diagonally to make a total of four corner squares.

Corner Squares Example - for 10" quilt blocks
10" block size x 1.41 = , 14.10" finished diagonal
Parent square size = 14.10" / 2 = 7.05" + .875" = 7.925, round up to 8"
Corner Triangle Parent Squares for Common Quilt Block Sizes

Corner Triangle Parent Squares for Common Quilt Block Sizes
4" blocks: use 3-3/4" parent squares
6" blocks: use 5-1/8" parent squares
9" blocks: use 7-1/4" parent squares
10" blocks: use 8" parent squares
12" blocks: use 9-3/8" parent squares
14" blocks: use 10-3/4" parent squares
15" blocks: use 11-1/2" parent squares
Let's Cut Setting Triangles
We'll cut a square twice diagonally to produce four setting triangles with the straight grain on their long edges.
1. Finished block size x 1.41 = finished length required on the triangle's longest edge. Round up to nearest 1/8".
2. Cut a square with sides that are 1-1/4" longer than the number in Step 1.
3. Cut the square in half twice diagonally.
Setting Triangle Parent Squares for Common Quilt Block Sizes
4" blocks: use 7" parent squares
6" blocks: use 9-3/4" parent squares
9" blocks: use 14" parent squares
10" blocks: use 15-3/8" parent squares
12" blocks: use 18-1/4" parent squares
15" blocks: use 22-1/2" parent squares
Setting Blocks
Squares of fabric placed between blocks are called setting blocks. Cut them to match the unfinished size of your quilt blocks.
Decimal to Fraction Chart - 1/8"
0.125 = 1/8"
0.250 = 2/8" or 1/4"
0.375 = 3/8"
0.500 = 4/8" or 2/4" or 1/2"
0.625 = 5/8"
0.75 = 6/8" or 3/4"
0.875 = 7/8"