Check out Eleanor Burns approach to making HSTs - look here: http://www.quiltinaday.com/RulerInst...UpIns_web.pdfg

There's also a method where you sew two long strips (WOF) right sides togetheron BOTH long edges and cut triangles from this strip, one cut on one side, the next on the opposite side - this is really quick, but requires a special ruler, I think.

The direction are on YouTube under Missouri Quilt....Be careful. This method results in bias edges on all sides, which in turn may cause uneven blocks...ask me how I know. There was a suggestion that if you did this method spray starch your squares heavily.

I do hst's using the thangles as it takes the math out. They come in all sizes and thangles isn't the only company that has them. They are paper patterns with the sewing lines printed on them and after you sew them just remove the paper. They come in all sizes.

calculating hst square
 

here is a site that helps with the calculation and gives you a visual. i use this method quite a bit. what i have found is that you measure the diagonal of the square size you want (i.e. 5" hst) and add 1/2" for seam allowance to that measurement. then cut the two squares that size. it's the same idea deemail laid out.

http://whipup.net/2011/03/17/guest-b...are-triangles/

What is "RST" and "HST"? Thanks

RST- right sides together

HST - half square triangles

I have had the best luck with this method. It also results in bias on the edges, however. I starch the fabric or use Best Press on it.

You do not need a special ruler. Any ruler that is marked with a 45 degree line will do. For the first cut, put the 45 degree line along the top edge of the sewn strip, for the second cut put the 45 degree line along the bottom edge of the sewn strip. Then, just take out the stitches at the top of each triangle.

Here is a chart I found online some time ago. I haven't tried all the sizes yet to confirm but the ones I did came out right. Hope this helps

Sq = hst

2 in = 1
2.5 = 1.5
3.5 = 2
4 = 2.5
5 = 3.5
6 = 4
7 = 4.5
8 = 5
8.5 = 5.5
9 = 6
10 = 7

Google half square triangle paper sheets, and you can download these free. Any finished size you want.