Thursday, January 26, 2012

Sew Half-Rectangle Triangles

Method 1

A few days ago, on 22 January, I showed you quilt designs using this wonky block.

 Caroll Drudy of Attic Window Quilt Shop liked my designs and tried making the block. She reported, "I had to make those rectangles several times before I got them to come out right."

Now, I think it would be great if you were to make a quilt or two using this block. And I don't want you to have trouble with the rectangles; so I'm going to show you how to sew them.

I am going to assume that you already have a favorite method of making half-square triangles and just show you how to make the half-rectangle triangles.

For this block the rectangles are twice as long as they are wide. This means that for a 6"x6" block the rectangles would have a finished size of 2"x 4". For a 9"x9" block the rectangles would have a finished size of 3"x6".

Note: The two rectangles are not the same; they are the mirror image of each other. This means you will need mirror image triangles as well.

1 The triangles are made two at a time.

Start with a piece of fabric that is 1" wider and 1" longer than the finished size of the rectangle. For 2"x4" triangles, finished size, start with a piece of white fabric 3"x5". For 3"x6" triangles, finished size, start with a piece of white fabric 4"x7".

Cut the fabric diagonally starting 1/4" down on one side and ending 1/4" up on the other.  I've drawn a line on the back of the fabric above to show were the cut goes.

The two triangles above are identical. They are not mirror image.

To make mirror image triangles you need to slope the cut the other way.

This will give you 4 white triangles. Which is enough for 2 blocks.

You need to cut 2 green triangles and 2 mirror image green triangles as well.

2 A green triangle and a white triangle sewn together make a rectangle.

Start with a green triangle and a white triangle that are the same. They must not be the mirror image of each other.

Place them right sides together so that the long sides line up.

The long sides are the same length and will line up exactly.

Sew a true 1/4" seam, not a scant one, along the long sides.

3 The rectangle needs to be trimmed.

Fold the triangles open and press the seams. I press my seams open; you may have other ideas.

You now have a rectangle that is 2 1/2" x almost 5".

You need to trim equal amounts off each end of the rectangle to make it 2 1/2" x4 1/2".
You also need to make mirror image rectangles using mirror image triangles.

To finish the block you need half-square triangles. For 6"x6"  blocks you need 2"x2" and 4"x4" half-square triangles, finished size. For 9"x9" blocks you need 3"x3" and 6"x6".

There is more than one way to make half-rectangle triangles. I'll show you a second way in my next post.


  1. Thanks for the tutorial. I really liked this block and would like to make some more and this will be so helpful for doing that. I'll have to link to your tutorial!

  2. I greatly appreciate your tutorial on this. There are many others on the internet that are not correct. This one works!

  3. Thanks for explaining this fully. Now I can do any finished size 2:1 because you explained the math and cutting so clearly. I will need to experiment with rectangles that are not 2:1 to see if the 1/4" holds true for them.

    1. SHLyman

      I posted 3 methods for making half rectangle triangles. My favorite is the third one using freezer paper because it is the most versatile and requires the least math.

      You can make any triangle you like by simple drawing it at its finished size.

      If you don't have freezer paper, try spraying some 505 glue onto paper.