How to Sew and Trim Half Rectangle Triangles

I remember the first time I saw a pattern with half rectangle triangles. I loved the pattern! I bought fabric to make the quilt and then bought the pattern. But when I saw the directions for sewing and cutting half rectangle triangles I thought "Yeah, like that is going to happen."

For beginning quilters some blocks can seem tedious and like a waste of time. That's what I thought, or maybe it's because the whole process was overwhelming to me that I decided to bail on that quilt. Since then I have learned to like, notice not love, half rectangle triangles.

So why I am writing a "how to" now? Good question. You see my quilt pattern, Little Three Creeks, uses half rectangle triangles for the creek portion of the quilt. I want to provide any other beginning, overwhelmed quilters the tools to confidently sew my patterns. So let's get this party started.

Measurements and Ratio

Generally HRTs (Half Rectangle Triangles) have a 1:2 ratio, meaning they are twice as long as they are wide when sewn into your quilt. This makes calculating all the numbers for cutting and trimming much easier.

I have made a little chart with some basic measurements for you below. But to do the math for a 1:2 ratio HRT simply first decide the finished size you want your HRT to be (the size the HRT will be after it is sewn into your quilt). Add 1 inch to the width and 2 inches to the length to know what size you will need to cut your rectangles.

Example: I want a finished 2 in. x 4 in. HRT. So my fabric cuts will be 3 in. x 6 in. After sewing the halves together I will trim the HRT to 1/2 in. larger (length and width) than I want the finished size to be. So trimmed size will be 2 1/2 in. x 4 1/2 in.

If that is really confusing for you then see the chart below:

 Finished Size Cut Size Trimmed Size
1 in. x 2 in. 2 in. x 4 in. 1 1/2 in. x 2 1/2 in.
2 in. x 4 in. 3 in. x 6 in. 2 1/2 in. x 4 1/2 in.
3 in. x 6 in. 4 in. x 8 in. 3 1/2 in. x 6 1/2 in.
4 in. x 8 in. 5 in. x 10 in. 4 1/2 in. x 8 1/2 in.
5 in. x 10 in. 6 in. x 12 in. 5 1/2 in. x 10 1/2 in.

Cutting and Sewing Your HRTs

One important thing to remember when sewing HRTs is that there are two different cuts. It's not like with a half square triangle where you can just turn the square and it will be the correct direction. HRTs are either the correct direction or they aren't. So before you make your diagonal cuts across the rectangles, make sure you know how many of each direction you need.

Let's start sewing!

Notice in the example below how the pieces are slightly offset? This is how we want the block to be when it's been sewn together. So offset the ends by about a 1/4 in.

Pin the HRT pieces offset, right sides together, and sew 1/4 in. on the long side.

Set the seam with your iron by giving it a nice press. Then, I like to finger press the HRT open before using my iron.


Now for the part I dreaded back in the day... trimming. I am going to show you how to use a regular straight edge ruler to trim your HRTs. Rulers are expensive and an investment. So I try to only buy specialty rulers if I really don't like trimming a certain block in quilting, or if I absolutely need it for a quilt.

There are several specialty rulers for trimming HRTs. I have not tried them but know that people love them. Here are a couple to look at if this is something you want to invest in:


Let's get started with our straight edge ruler.

First, use your ruler to trim a little off each side to get the HRT to the desired width. We are continuing with the example from the cutting directions of a 2 in. x 4 in. HRT. So in this case trim the unit to 2 1/2 in. wide.


Second, line up the edge of your ruler with the left side of your HRT. Side the ruler down until the intersection of the 1/4 in. mark lines up with the diagonal seam. Trim across the top.

Next, flip the HRT around to do the other side. Line up the edge of the ruler with the edge of the HRT. Slide the ruler down so the 1/4 in. mark lines up with the diagonal seam and the end of the HRT touches the line of the desired length. Trim excess off the top.

Below is my trimmed half rectangle triangle measuring 2 1/2 in. x 4 1/2 in. It's ready to be sewn into my quilt for a finished size of 2 in. x 4 in.


Trimming HRT can be a bit tedious and attention to detail is required. However, the finished product is quite satisfying. Little Three Creeks is one of my favorite patterns and if I hadn't gotten over my fear of HRTs it never would have been designed. Try is out and let me know how it goes.



Above you can see all the HRT I did for the baby version of Little Three Creeks. The final result is so worth the time, sewing and trimming.


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