Half square triangles are one of my favorite quilt blocks! Half Square Triangles are square quilt blocks made from two right-angled triangles of different fabrics. They are very easy to make and you can create a ton of great simple, modern designs just by combining different colors and sizes of an HST block. I'll walk you through the basics of creating this block.
What you will need:
- Quilting fabric, ideally 2 different colors
- Ruler, ideally a square quilting ruler
- Rotary cutter or fabric scissors
- Fabric marker
Cut out your squares
HST blocks start with 2 squares.
If you're creating a pattern, it probably specifies the size of the squares you'll need to cut for the half-square triangular blocks. If you don't use a template, you will have to calculate it yourself. The general rule of thumb is to measure 7/8″ from the size of the final block once it is in the quilt. So if a block measures 5″ when sewn, you should start with a 5 and 7/8″ square.
If you prefer to start with larger squares and scale down to the final size, you can add an additional 1/8″ or 1/4″ to this 7/8″ rule of thumb.
Half Square Triangle Cheat Sheet
Make half square triangles – 2 at a time
Step 1: Sew Together
Place the two fabric squares right sides together, aligning the edges. With a fabric marker, draw a diagonal line from one corner to the opposite corner using a ruler as a guide. This line will be your sewing guide.
Sew a seam on each side of the seam guide you drew using a 1/4″ seam allowance. Your square should have 2 seams with the seam guide line directly in between.
Step 2: Cut along the marked line
Use a rotary cutter or scissors to cut out the seam guide you drew. You should now have two rooms that open into half-square triangular blocks.
Step 3: Tap
Then press your HST. I usually iron my seam allowances toward the darker fabric so they are less visible, but some designs may require open seams.
Step 4: Measure and Cut
The final step in preparing your HSTs is to square them and make sure they are the size you want. To do this, you will use your ruler and rotary cutter. Place the 45 degree line of your ruler on the diagonal seam of your HST. Using the 45 degree line will ensure perfect stitches on your triangles in the quilt. Check that your HST measures correctly on all sides, then cut off any excess fabric.
You should now have 2 half-square triangular blocks. Congratulations!