A half-square triangle, or HST, is a common quilting term for a square made up of two triangles joined together on the diagonal. It is one of the most common units of a quilt block, probably second only to a plain square. They are used in many quilt blocks, like the shoo fly or the churn dash. There are many ways to make these, but this method is the easiest one ever.
Cut squares of fabric
Begin with two identical squares. Make them each the same size that you want the final square to be. For example, if you want to make 3-1/2″ squares, cut each of these 3-1/2″ square. When you join it with other pieces, it will finish at 3″ since it has the standard 1/4″ seam allowance on all sides.
Mark with a diagonal line
Lay the squares right sides together. Using a ruler, draw a diagonal line from one corner to the opposite corner.
Sew right on this line.
Trim off one of the sides (it doesn’t really matter which one).
Open and press the seam to the dark side. The square should be accurate to the original size that you cut.
What is good about this method
- The math is super simple – just add the regular 1/2″ seam allowance for the square.
- No dog ears (tiny triangles sticking off the corners)
- No trimming to size – it’s automatically the right size.
What isn’t good
- There’s a lot of waste fabric. The cut-off side of the square is waste. You can join them to make a smaller HST block, but it’s unusual to have a pattern that will use both sizes. More often than not, they become “bonus” pieces that go into your stash waiting to be used in a new project. If that’s what you want, it’s fine, but for some people it’s more stressful.
Rating: 3 out of 5
I think this method is great for beginners or people who struggle with arithmetic. It works if you are in a hurry and have lots of fabric to spare, but it is not my favourite method.