I want the finished size of a hst to be 2 1/2 inches. I though by cutting 3 inch squares then in half would work, but the pieces are looking tiny to me. Do I need to make them bigger? How much bigger? For this quilt I can cut down the rectangles and add extra borders. It's a quilt my brother designed and it looked kind of easy once I fixed it.

For HST add 7/8" for QST add 1 1/4"

hst add 7/8"
qst add 1-1/4"

The "magic number" for half-square triangles is 7/8". You simply add 7/8" to the required FINISHED SIZE of your half-square triangle unit.

Here's a good link:

http://www.patchwork-and-quilting.co...triangles.html

wonderful. I guess I'll just use them in something else and recut those triangles. They're gonna be way to small

Thanks for the replies!

in case you still are not sure- to finish at 2 1/2" your squares need to start at 3 3/8" (2 1/2 + 7/8)

7/8 IS the correct addition but I add an inch so I can square them up afterwards. Makes a big difference to the accuracy when you want to join them nicely!

I always add the 7/8 plus a little more. Better to trim then lose the whole block.

Thanks...