Half Square Triangles and Postcard Patterns

Putting entire patterns onto postcards is my specialty. And I love it! There’s no fluff to get lost in. Just what you need and nothing else. Many patterns are too complex for this, but it’s amazing what you can comfortably explain in such a short space. (It’s also amazing what little things can take up a surprisingly large amount of space, but that’s a story for another day)

The flip side to this no frills approach to pattern writing is that it has to be assumed that the person sewing on the other end already knows certain things about quilting. Like, “sew fabrics right sides together with a 1/4” seam allowance.” And 99% of the time that works out great. But sometimes there are questions (and I’m happy to answer).

The most common questions I get are about half square triangles (HSTs) and their sizes. Most quilters know that squares finishes 1/2” smaller than cut (you lose 1/4” on each side from the seam allowance) so a 5 1/2” cut square will finish at 5”, a 4 1/2” square at 4” and so on. But what is the rule for HSTs? With the method I use (diagramed below), HSTs finish 7/8” smaller than the cut size. So to get a 5” HST, we would cut 2- 5 7/8” squares. Anytime you see a square cut to a size that ends in 7/8” to be used in making HSTs, the finished HST triangle size is 7/8” smaller than the cut squares.

Mark a diagonal line down the back of one square. Sew right sides together 1/4” on either side of the line. Cut apart along the line & press open.

Mark a diagonal line down the back of one square. Sew right sides together 1/4” on either side of the line. Cut apart along the line & press open.

For the sake of space (and because for a long time I resisted the idea that squaring up blocks was a necessary part of quilting), I will often just give the exact measurement needed. Quilters who like extra room to square up simply round up their preferred amount and square down if they choose to. For example cutting 6” squares to work with, then squaring to 5 1/2” after sewing & cutting the diagonal to get 5” finished HSTs; rather than cutting the 5 7/8” called for in the pattern and skipping the squaring up. I’ve learned that there are many opinions on how much to round up, but the extra 1/8” is usually plenty for me.

Years of quilting have taught me that squaring really is worth the effort. So if I can squeeze it in, newer patterns usually have you cut larger and tell you to square up.

The only exception to these rules are a few older patterns that are entirely HSTs sewn together. It doesn’t matter what size the HSTs finish at as long as they’re all the same. So I save the 7/8” headache and cut at a round number but still don’t square. This will leave you with odd finished block sizes like 8 1/8” square, but that really doesn’t matter. If you want a more clean finish, I suggest adding in the unwritten step of squaring the HSTs to a slightly smaller size after sewing. For example, if you cut the squares 9” you would square to 8 1/2” after sewing and then finish with 8” HSTs.

And of course there are a million other ways to make HSTs out in the universe that don’t subscribe to these rules at all. Many involve paper, bias edges on the outside, special templates and other things that don’t easily fit on a card. I love my method of choice because it leaves the bias in the middle (stretchy edges are no fun), it’s easy to explain in a little space, and it’s very scrappy friendly.

Hope that clears up your HST questions. Let me know if there is anything else you’d like to know!

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