Estimated reading time: 5 minutes

Half-square triangle blocks are easy to make.

However, these tips for half-square triangle blocks can really help the beginning quilter to understand how and why you need to square your units or blocks accurately. I know they helped me!

There are lots of techniques for making these blocks. This one describes how to make them individually versus mass-produced, in case you don’t need 200!

Start your half-square triangle block with two squares.

Image of Two Fabric Squares

For example, shown above are two 4-inch squares of fabric. One is a dark gray batik. The other is a soft white.

The block we need will be 3 1/2″ (before sewing to other units). The actual “finished” block size will be 3 inches. Therefore, above you see two 4-inch squares. Draw a diagonal line, corner to corner, on the reverse side of the lightest fabric.

Draw a diagonal line from corner to corner on the light square.

While it doesn’t really matter which fabric you choose, you’ll follow this line as a guide for stitching. Just make sure you can see your marking well.

Stitch on both sides of the marked line.

Layer your squares with the marked one on top; I’ll say “right sides together”. However, remember that if you are using BOTH beautiful sides of fabric in a half-square triangle block, you’ll want your “intended fronts together”. This means BOTH right sides will either be facing down or facing up.

Next, stitch from corner to corner, 1/4 inch from the drawn line.

Image of Block with Stitching

Make great time by chain-stitching.

If you have lots of these units to make, try chain-stitching them. First, have your squares marked and paired, ready to stitch. Second, stitch on one side of the line on each set, without cutting threads in between. Thirdly, turn the string of them to repeat the stitching on the other side of the line.

Cut on the center line.

Separate the units by snipping the threads. See “Two Purple Tools for Quilting” for a great cutting tool. Press to the darker fabric. The block should be larger than 3 1/2 inches and have threads and tails (or ears) on them as shown below.

Image of Block and Ruler

Use a squaring ruler with a 45 degree line.

Using any ruler with a 45-degree line, place that line along the diagonal seam of your block and so that the over-all size after you trim the first two sides is still slightly larger than 3 1/2″. Notice the extra fabric outside of the 3 1/2″ marks?

Don’t trim the first two sides at the 3 1/2 inch mark.

Trim the first two sides slightly larger than 3 1/2 inches. This will allow you to get the most accurate finished unit with a perfectly aligned diagonal seam.

Image of Last Cut for Block

Next, spin your half-square triangle block around and line up the trimmed sides directly on the 3 1/2″ marks. Trim the last two sides.

I AM from the Show-Me State!

Perhaps most new quilters would figure out on their own not to make the first trim at exactly 3 1/2 inches, but I needed a kind teacher to show me why I shouldn’t so that with the first trimming cuts.

If you are making the River Heritage Block-of-the-Month Mystery Quilt, you are probably figuring out that there are a lot of half-square triangle blocks  in the design.

Here is a the Trail of Tears block, featuring all half-square units.

SHOP more than 50 quilt patterns that use BOTH beautiful sides of fabric!

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