The half square triangle, also referred to as HST, is a common block in traditional, modern and contemporary quilting. Use it alone or combine it with other quilt blocks to form more complex patterns for a quilt. This block is a popular ‘stash buster’ to use up scraps of fabrics from other quilting or sewing projects.
What is a Half Square Triangle Block?
Half square triangle is a quilt block with two 90-degree triangles, where each of the triangles is half of the square, divided diagonally. In this article, we’ll show you the basics of half square triangles and how to sew two triangles together. There are several other methods for making half square triangles that are easier and more accurate. See our article Seven Ways to Make Half Square Triangles (HST) for easy instructions on other methods.
When you use the basic method starting with two triangles (shown below), the long diagonal edges cut on the bias can stretch if over-handled. My favorite method is Half Square Triangles Two at a Time. In this method, you first sew two squares together, then cut them down the middle. The stitches stabilize the bias, so no fiddling with stretchy bias edges.
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Half Square Triangle Calculator
Okay, this is when you wish you had paid more attention in geometry class! No worries, we’ve got you covered with this easy formula and cheat sheet for how to cut your fabric for half square triangles.
Start with the size you want your finished quilt block to be. We’ll use the example of a 3″ finished quilt block, which means your sewn half square triangle block will be 3-1/2″ to allow for a 1/4″ seam allowance on all sides. You’ll want a right triangle, where the corner is 90 degrees. To accommodate the center diagonal seam, we’ll cut the length and height of each triangle at 7/8″ larger than the desired finished size, and then cut diagonally from both points. Below is a picture of how to cut the center line with special ruler made by Bonnie Hunter with markings that match the finished block size,
Here is a cheatsheet on the length and width for the right angle for different size finished half square triangle blocks:
- 1″ finished blocks, cut the length and width 1-7/8″
- 2″ finished blocks, cut the length and width 2-7/8″
- 3″ finished blocks, cut the length and width 3-7/8″
- 4″ finished blocks, cut the length and width 4-7/8″
- And so on — cut the length and width 7/8″ larger than the finished block size
Browse through more quilt inspiration and projects on Create Whimsy.
- See how to make half square triangles two at a time – PREFERRED METHOD
- See how to make half square triangles four at a time
- See how to make half square triangles eight at a time – PREFERRED METHID
- See how to make half square triangles from a jelly roll
- See how to make half square triangles from a layer cake
- See how to make half square triangles from a charm pack