Originally Posted by lee_stitches
Pythagorean Theorem? A squared + B squared = C squared is the formula for a right triangle. 8 squared + 8 squared = C squared. 64 + 64 = C squared. 128 = C squared. The square root of 128 = 11.3
You need to add in the seam allowance before doing the math. So the 8" finished block becomes 8.5". Plugged into the formula, you get 12.02. Just to demonstrate that you can use the formula OR the "Multiplying by 1.414" trick, multiplying gives you 12.019. Round UP to the nearest 1/8 for ease in cutting, so sashing strips would need to be cut at 12 1/8.