How to Do the Math to Cut out 8 Half Square Triangles
We have been asked a number of times, how to calculate the size of the starting pieces of fabric when you want to cut 8 Half Square Triangles at the one time. So here it is. We also have a video below on how to cut the 8 half square triangles.
Calculation to work out the size of the starting fabric:
The size of your finished block + 7/8″) x 2 = size of starting fabric
For example if you want your finished block to be 2 1/2″ your calculation will be:
- (2 ½” + 7/8″) x 2 = 6 ¾” (we round up to 7″ – see note below)
So the size of the square that you need to start with is 6 ¾”
This will result in 8 unfinished squares that are 3″ each. When you sew them into the project you will be using a ¼” seam which will bring the size of the block down to a finished size of 2½”.
In the following video, we show you how to cut half-square triangles. One of these methods is the ‘How to Cut 8 Half Square Triangles’ technique. It’s a great way of cutting lots of half-square triangles quickly.
Scroll through to the 5-minute mark for the information on cutting 8 half square triangles.