I am attempting a block where I want to add a half square triangle on the sides. Can anyone please tell me how to calculate the size of square I would need to get a half square triangle by cutting it in half?

Thank you,
Pat

add 7/8ths of an inch to the size of the finished square.

Pat,

Handle the bias edge of your square carefully. Bias stretches.

Perhaps Patrice can give you another measurement wherein you could cut your square into quarters. This way your bias edge will be stabilized by your other blocks.

Suzanne

When I make a half sq triangle I always cut a square 1 inch larger than what I want the finished block to be. Put two pcs together and draw a line diagonally across. Sew on either side and cut on the drawn line. Press open and viola, you have two half sq. triangles. Then square them up to the correct size. For instance, if you want a 2 in. finished sq. Cut a 3 inch block. After sewing and cutting in half, you would sq. it up to 2 1/2 inch because that would be with the seam allowance/ HOpe this helps. Marge

If you want to make lots of half sqs. use Eleanors Burns method.
for 2 1/2 in. use 2- 6inch squares right sides togather. Mark an x with a pencil and sew 1/4 inch on each side. Cut 3in in from each side then thru the middle of the x lines. Square up. You will have 8 half sqs. For 3 1/2 use an 8 inch sq. You can easily judge size this way.
If you only need 4 use a strip 6 x 3 draw a line at 3in then draw a line from corner to corner on each side of line so it looks like a v with a line thru the middle. Sew on both sides of v line. Cut at the 3in line then between the v line. This is hard to explain without pictures but it is very simple. This method only needs a small amount cut off for squaring up.
If you have high speed internet I recommend watchin video on Qnntv. It show Burns all day every hr on Thurs. And Fons and Porter all day Weds.