When you need lots of identical half square triangles (HST) and want them fast, make eight at a time!

With this easy and quick method, you can mass produce blocks, and the outside edges are all on stable straight-of-grain – no bias edges! So if you have a quilt pattern with lots of matching half square triangles, this technique is perfect.

Check out our article that shows seven (7) different ways to make half square triangles.

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Half Square Triangles Eight at a Time Block Calculator

With some easy math, you can make any size HSTs for your next project! Just use this formula. (See common sizes listed below for quick reference.)

To calculate any size HST: Start with your finished block size and add 7/8″, then multiply by two. (Finished block size + 7/8″) x 2 = size to cut fabric squares. Cut two contrasting squares for each set of eight (8) half square triangles.

2″ finished block: (2 + 7/8) x 2 = 5-3/4. Cut two squares at 5-3/4″ to make eight (8) 2″ finished half square triangle blocks.
3″ finished block: (3 + 7/8) x 2 = 7-3/4. Cut two squares at 7-3/4″ to make eight (8) 3″ finished half square triangle blocks.
4″ finished block: (4 + 7/8) x 2 = 9-3/4. Cut two squares at 9-3/4″ to make eight (8) 4″ finished half square triangle blocks.
5″ finished block: (5 + 7/8) x 2 = 11-3/4. Cut two squares at 11-3/4″ to make eight (8) 5″ finished half square triangle blocks.
6″ finished block: (6 + 7/8) x 2 = 13-3/4. Cut two squares at 13-3/4″ to make eight (8) 6″ finished half square triangle blocks.
And, so on.

Makes eight (8) half square triangles

How to Make Half Square Triangles Eight at a Time

Prep Time: 10 minutes

Active Time: 20 minutes

Total Time: 30 minutes

Half square triangles are a traditional quilt block, and are also used often in modern and contemporary quilts. This technique makes eight half square triangles at once from two fabrics.

Materials

2 squares of fabric cut to the right size for your finished block (see chart above)
Thread to blend with fabric

Tools

Sewing machine
Rotary cutter
Rotary mat
Iron
Ironing board
Frixion pen, or other fabric marker

Instructions

Cut two squares from your fabric for your finished block, see chart above. I wanted 3" finished blocks so I cut 7-3/4" squares. Draw diagonal lines on one of the blocks with a fabric marker. I used a Frixion Pen. You'll position the marked side up for sewing.
I like to line up my pieces perfectly and secure with pins so they stay straight while sewing.
Sew 1/4" to one side of the marked line with your 1/4" foot on your machine. On a Bernina it is the 37 or 57 foot.
Turn and sew 1/4" from the same line on the other side of the marked line..
Now sew 1/4" from the other line.
Turn and sew the final 1/4" seam.
To make the first cut, cut right down the middle of the square, right where the lines and seams intersect in the middle.
Turn, and make the second cut again right down the middle of the where the lines and seams intersect, making four pieces.
Cut each piece on the marked line to make eight (8) half square triangles.
Finished eight (8) half square triangles ready for a project!