Originally Posted by MTS

The "exact" formulas:

For the HST:
Starting squares - add 7/8" to the FINISHED size, cut in half on the diagonal.

For the QST:
Starting squares - add 1.25" to the FINISHED size, cut twice on the diagonal.
However, you can make the HST (draw diagonal, sew either side, cut apart) and then cut that in half.
Depends on how scrappy your color choices - if they're all going to be green and yellow or pairs of colors, then make the HST.

These triangles will all have straight edges on the outside of the blocks - no bias.

I prefer to start with larger squares, make the blocks, and then trim down to the UNFINISHED size.

HTH.