I like to make 8 HST at a time. The only drawback to this method is that they will all be identical. Here is my formula:
Half Square Triangles cutting 8 at a time
Use two same-size squares to make multiple triangle-squares.)
To determine what size squares you need to cut, multiply the desired finished size of the triangle-square by two, then add 1 ¾ “. For example, for a finished triangle-square that is 2 ½”square, use 6 ¾” 2 X 2 ½ (finished size) = 5”
5” + 1 ¾” = 6 ¾” square
Bisect the square in half in both directions with a pencil and a ruler and then draw the diagonals. Sew 1/4 inch on either side of the diagonal lines and cut apart on the vertical and horizontal lines. You will have 8 half square triangles.