In December of 2011, I posted this video as a Countdown to Christmas tutorial:

Absolutely LOVED the idea and practiced it many times.  Problem was, I couldn’t get the FORMULA figured out.  You know, the formula for making the half-square triangles the size needed for various quilt projects.  I searched and searched online for someone who knew the secret formula but never did find it.

This past weekend, I needed to make a number of half-square triangles and I was bound and determined to figure that elusive formula out.

I needed 5 1/2″ unfinished half-square triangles.  My first practice piece was made using a 2 1/2″ increase in the 5 1/2″ unfinished size I needed – so, the squares were 8″.

Once cut apart, I was still loving the much simpler technique for making half-square triangles!  But alas, the size was incorrect as I ended up with 5″ half-square triangles instead of 5 1/2″ ones that were my goal.

But, those measurements obviously meant I was on the right track!  The next size I tested was 3″ bigger than my goal so I used 8 1/2″ squares.

The results – PERFECTO!

And to finish out my half-square triangle success, I squared up the blocks and the results were so darned perfect I almost jumped for joy!

So now, the secret is no longer a secret to me.  To make half-square triangles using the method shown in the video above, you need to add 3″ to the size of your unfinished squares.  It sure made my piecing go very quickly once I had the formula figured out!