Making half-square triangles with the Most Popular Method

This method of making half square triangle units has been around for a long time.  It is very popular, and for good reason.  It is pretty simple and eliminates the waste that occurs when doing one unit at a time.

A half-square triangle unit is made with two right angle triangles sewn together on the diagonal to make a square.

This method is not intuitive, but it’s easy once you learn it.

See it all

Below you will find:

• video tutorial
• written tutorial with pictures
• evaluation of this method
• blocks that use half-square trianges
• quilts that use half-square triangles

Tutorial

Follow these steps to get perfect triangle units.

Cut fabric squares

For this method, you need two squares, each an inch larger than the finished size you want.  (The finishes size is the size it will be in the quilt, not including seam allowances.)

For example, if you want 4″ units, cut 5″ squares.

If you are VERY accurate, you can get away with only adding 7/8″, but this doesn’t leave you any room for error.  Most people prefer to make it a bit bigger, and trim off the extra later.

Mark a diagonal line

Place the two squares right sides together.  On the back of one side, mark a line from corner to corner on the diagonal.

Stitch

Sew 1/4” away from the diagonal line on each side. 

Option 1: If it is easier, you can mark the lines 1/4” away from the centre diagonal and then sew right on the lines. This will help sewing be more accurate, but you have to mark twice as many lines.

Option 2: If you don’t want to mark any lines, you can always mark a 1/4″ line on your sewing machine with tape or a laser light and align the centre of the square with that line while stitching. It is best to do this only you have some experience.

Cut

Cut between the lines.  The cutting doesn’t have to be 100% accurate, since the sewing is already done.

Press

Open and press the seam allowances to the dark side.

Trim

Lay your ruler on top of the square, making sure the diagonal line lines up with a 45* line on the ruler.  Shave the edges off the sides to get it down to the size you need. In this case it’s 4-1/2” (finished 4” square plus 1/2” seam allowances”.

This is called “squaring up” since it gives you a chance to compensate for any potential stretching that happens when you sew along the bias.  You end up with a perfectly square piece with the diagonal in the centre.

If you do a lot of half square triangles, there are specialty rulers you can get to help with this step, but I’ve never tried them.  I have no problem with my regular rulers.

Trimming also removes the dog ears. Here they are – two perfect units.

Evaluation of the Most Popular HST Method

When to use this method

• If you are using pre-cut squares
• You need a lot of HSTs
• You need an odd size

Rating: 4 out of 5

This is one of my go-to methods for making HSTs.  It is a forgiving method. Even if your cutting and stitching is not totally precise, you can still get a perfect result.

I used this method in my Rolling Meadows quilt.  It is easy enough for beginners, but experienced quilters still use it.

Blocks with half-square triangles

Use HST units in these quilt blocks. Click on the links to see tutorials.

Friendship Star

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Churn Dash

Shoo Fly

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Algonquin Charm

Quilts with half-square triangles

No Flies in my Garden

No Flies in my Garden has shoo fly blocks surrounded by chain blocks.

Twinkle Sampler – large

This green and pink quilt is the large version of the Twinkle Sampler Quilt pattern.

Nine Patch Sampler Quilt

This quilt is a Nine Patch Sampler Quilt. Each of the blocks are variations of the traditional nine patch block.

Scrappy Twinkle

This scrappy quilt is the medium sized option in the Twinkle Sampler pattern.

Making Memories

Making Memories is an easy quilt pattern made with squares and half-square triangles.