I know that there is a formula for cutting squares to make half square triangles. It seems that you make it either 5/8" larger or 3/8...????... I can't recall. If anyone knows the formula, please let me know. If I'm not being clear, it's the sq. you cut and draw a diagional line through the center, corner to corner and sew 1/4" seam on either side to give you 2 half square triangles. Can anyone help me????

If you want a 4 1/2 square, start with two 4 7/8 squares, right side together, draw the line in the middle and sew 1/4 inch away from both sides of the drawn line. Open and you have two 4 1/2 squares.

I learned with 5 in. squares. Then after you mark, stitch and cut apart, you square them to 4 1/2 inches.

I do it like Inordyke said. Better to be a little to big and square up rather then worry about an exact 1/4 in. seam.

I use the 1" larger than the finished HST as my guide and trim. So if my finished HST is 4" I start with a 5" square. I draw the sewing lines 1/4" from the center and sew on them, cut down the center and press both sides open. Using this method you do have to trim each HST on all 4 sides but it makes for a nicer square. It also eliminates the need for the perfect scant 1/4" seam.

There is also a wonderful HST Tutorial by Rhonda and she uses a totally different method. It may work for you.
http://www.quiltingboard.com/t-37915-1.htm

I'm with Mad. 1 inch larger squares than the size of HST I want.

I totally cheat n use paper piece, like triangulations

I go bigger, then trim. If you want a 4.5" square and then do a 4 7/8 with 1/4" seams, right off the bat aren't you pulling it in MORE than 1/2 inch? Because of the angle?

Anyhoo, I'm just not that accurate. I'd rather sew, sew, sew and then trim, trim, trim. I've tried to do it the other way and ended up sew, sew, sewing some more...

exactly, skip the 5/8 or 7/8th..to hard to find on the ruler and the mat..just go 1 inch bigger..

Thanks everyone for the help...Now gotta' get 'er done...