Half-square triangles, or HSTs, are one of my favorite block pieces to make! They are incredibly versatile and fun. I'm going to show you how to get perfect half-square triangles every time. I also have a cheat sheet for you of many sizes for 8 at a time HSTs. This is located at the end of this post, but if you want to download it, you can do that here.
Let's get started!
1. Begin by cutting the size squares required the size of half square triangle you want. For this tutorial, I am making 2.5" x 2.5" unfinished squares, because my newest pattern about to be released uses these. This requires (2) 6" x 6" squares. Use (1) square of each color.
2. On the wrong side of (1) square, draw two diagonal lines, from corner to corner. You can use a water soluble or heat erasable pen, a hera marker, or a pencil. 
3. Place both squares right sides together. Pin in place.
4. Sew a ¼" away from BOTH sides of the drawn lines.
5. Cut along the drawn diagonal lines, as well as vertically and horizontally down the center.
6. You should have (8) half-square triangles with dog ears. There are two ways you can go about this next part:
I highly recommend the Clearly Perfect Slotted Trimmers by New Leaf Stitches. The set of two rulers covers many sizes of HSTs and allows you to trim them before you press them open. I have been using these for years and love them! It definitely makes my sizing more accurate and gets the job done much quicker.
To use this ruler, you will line up your 2.5" line with the stitches of your seam. Trim away the excess. You can trim off the dog ears using the slots on the sides of the ruler. Press open and you will have a perfect 2.5" x 2.5" HST. 
OR
If you don't have a slotted ruler, no problem! You will take your untrimmed HSTs and press them open. Choose an appropriately sized quilting ruler with a 45° diagonal line. Line up your HST in the corner, aligning the diagonal line with your diagonal seam. Make sure your HST extends past the 2.5" ruler lines on the left and bottom sides. 
Trim away excess.
Next, flip that HST 180°, this time lining up the trimmed edges exactly with the 2.5" ruler lines. The diagonal seam should again line up with the diagonal line on the ruler. 
Trim away excess.
Repeat for the rest of your HSTs and there you have it! A simple, efficient way to make 8 HSTs at a time.
