HSTs come up alot.
After years of trying different methods even wasting $23 on Triangulations, which uses paper grids, I find that Eleanor Burns method is by far the best. Quilt in a Day triangle square up ruler is at Joanns and with a coupon it is less than $10.
You do need her triangle square up ruler, it is the best tool I have. With it you can square up with just one cut.
For making 8 HST at a time you use two squares right sides togather. For 2 1/2 in squares use two 6 in squares. Just add two inchs for the next size up. 8 in for 3 1/2 in squares etc.
Just draw an x on the sq then sew 1/4 in down each side of lines. Cut the sq in half each way then on drawn lines to get 8 HSTs. Then with the ruler make one cut to square up.