How to Make Four Half-Square Triangle Quilt Blocks at One Time (with no marking!)
Here’s a quick way to make four half-square triangle quilt blocks from two fabric squares.
Start with two same-size squares. Mine were 10″, the size square that comes in layer cake precut packages.
Lay the squares with right sides together. Carefully align the edges and corners. 
Sew all around the outside of the squares, using a scant 1/4 seam allowance.
Use your rotary cutter and ruler to cut the squares in half diagonally in both directions.
You will have four triangle blocks.
Press the seam allowances to the side of the darker fabric. You will get four identical triangle blocks with little tails at two corners.
Use a square ruler (if you have one) to trim off the tails and if necessary, trim the block down to the exact size you want. My squares were 6-3/4″, so I trimmed them down to a more useful 6-1/2″.
When you do the 4 triangle method, don’t you end up with the straight side of the HST being on the bias? I would think that would make distortion easier when you sew them together…
Yes, it’s true that this method makes stretching more of a possibility than some other methods of making half-square triangles. I haven’t found that to be a problem, but it’s definitely a weakness of the method.
Thank you for the tips. I avoid hst’s because they never come out the same for me. I’m going to try these out!
I understand how to make hst triangles, what I dont understand is what size squares u start with to get there. large hst vs 4 hst. thanks Eileen – couldnt find anything relating to the math equations u talked abt
Thanks for the question, Eileen. When you use this method (sewing and cutting a pair of squares into four half-square triangles at one time), you can start with any size squares you want. I used 10″ squares in my sample. The four triangles came out at 6-3/4″, which I trimmed down to a more useful 6-1/2″, for a finished size of 6″.
If you use the two-squares method, I start with squares that are 1″ larger than the finished size triangle block I want. Getting to the finished size requires trimming the triangle blocks after you sew them.
Hope this helps.
If I want a 10 inch finished square what do I need to do. Do I simply sew diagonally and cut Would I then have 2 pieces instead of 4 to make the finished 10inches. I have no vision. Sorry.
Hi Charlene,
I’m on the road right now, so don’t have access to all my quilting math info. The simplest way to get 10″ finished triangle blocks is to use the two-squares method. The link will take you to our blog post on how to make the blocks that way. Start with two 11″ squares, then follow the instructions in the blog post. Each set of two squares will produce two finished triangle blocks. Sorry for the short answer! Hope it helps.
I did this method just last month. Worked out I want 10in finished blocks. So worked out I needed 50 of each colour for what I needed but forgot I had four blocks from one so now have 4 times the blocks instead of 100 I have 400. Just watch your maths
Ouch! But I’m sure you will find a use for all those blocks.
I liked the short cuts! Thank you ! Rita
I don’t understand ? Do you fold the 10″ squares ?
Lay the squares with right sides together. Carefully align the edges and corners.
Photo of two fabric squares with right sides togetherSave
Sew all around the outside of the squares, using a scant 1/4 seam allowance.
Hi Sandra,
No, you don’t fold the squares before you stitch them — lay two squares with right sides together and sides and corners aligned, then stitch all around the outside. Let us know if this still doesn’t make sense.