I found some instructions and a chart for the Magic 8 HSTs up to 6" finished:

To make a Magic 8, first determine what size finished half square triangles are desired. For example: To make 2" finished half square triangles, Add to the 2" measurement, 7/8". Your total is now 2-7/8" Multiply 2-7/8" by 2. That equals 5-3/4". (2) 5-3/4" fabric squares are the size needed to create (8) 2" finished half square triangles.
** improvement: cut the 2 fabric squares 1/4" larger. For the above example...Cut (2) 6" squares instead of 5-3/4". This will allow you to trim your half square triangles for more accuracy. For those very accurate quilters, this step may not be necessary.

Quote Originally Posted by rebeccas-sewing View Post
What would be awesome is a chart for making 8 HST's at a time. Just drawing on the lines doesn't take that long and ending up with 8 instead of 4 HST's makes that added steps worthwhile to me. Also, you don't end up with bias on the edges. https://www.youtube.com/watch?v=saBKMqyw-0E