The Quarantine Quilt – Week 3 – Half Square Triangles

Welcome to Week 3 in the Quarantine Quilt Project Series!  This week we will be learning how to make a half square triangle (HST) and we will put them all together in a simple 16 square block, like this:

If you missed the Intro post, make sure to catch up here!

And now that you have some good practice lining up your corners and sewing more precise seams from the 16 square block and the knot block , let’s get started on the half square triangles block!

Here’s what you will need:

  • fabric – 16  4 1/2″ squares (8 from white or other main fabric, 8 from other fabrics)
    • for my block, I picked 4 different fabrics so that I could have 2 squares of each for a total of 8 squares, then the other 8 squares are white
    • you could also have maybe 8 squares of white or your main fabric, and 4 squares from two different fabrics
  • a 4 1/2″ square template – you can again make your own, or you can buy a plastic quilting version
  • a 3 1/2″ square template – you will already have this from the last couple of blocks
  • seam gauge
  • Pilot Frixion pen, or other marking tool
  • ruler


1.  Cut out your 4 1/2″ squares.  Make sure you are using the bigger 4 1/2″ template – we will be cutting them down to the smaller size once we make our half square triangles (HST’s).  When you are done, you will have 16 squares total.  8 of mine are white, and then I have 2 of each of the four colored fabrics.

2.  Start making half square triangles (HST’s).  To make a HST, take a white square and one of your other fabric squares and place them right sides together.

First we are going to draw a line with our marking tool and ruler from one corner to the other.

Now we are going to use our seam gauge to measure 1/4″ away from the line you just drew on both sides.  These are going to be our sewing lines actually.

If you would like to keep your squares more secure, you can pin them together. Make sure they are lined up and sew down the two outer lines (but NOT down the center line!)

This is what it will look like…

Now cut down the center diagonal line in between the two lines you just stitched.

And now you have two half square triangles!  Don’t worry about the little thingies hanging off the corners – we will be trimming them down later!

Continue with the rest of your squares, combining a white square with a colored fabric square, always sewing right sides together.  Mark your diagonal line, mark your sewing lines 1/4″ away from that diagonal line on both sides, sew on those lines, and cut down the diagonal.

You will then have 16 of these…

Take them to the iron and press the seams on the back first, then on the front so that everything lays nice and flat.  I like to press my seams toward the darker fabric especially when I am using white as the other color, so that you can’t see through it as much.

3.  Trim down the HST’s.  If you were doing a whole quilt of broken dishes blocks or half square triangles of this size, you would only need to trim off the little bits hanging off the corners so that the squares would be even.  But we are going to trim ours down a little more because we are wanting all the different blocks in our sampler quilt to end up being the same size.  Each little square will need to be 3 1/2″ to match the squares in the other blocks we’ve done.

So take out the 3 1/2″ square template and place it on top of your HST so that both corners line up right on the diagonal.

If you are using a plastic template, you could use a rotary cutter to trim these and that would go a lot faster!  Or you can do what I did here and trace around your template, then cut out the square with scissors.

Do the same thing for the rest of your HST’s, trimming them down to 3 1/2″, and just make sure when you line up your template that those corners are right on the diagonal!

Then you will have 16 finished HST’s that are 3 1/2″ square!

4.  Lay out your HST’s in the block.  So before we lay out our half square triangle block, I want to show you how fun and versatile HST’s are!  They can be arranged in so many different ways to make so many different blocks.  I took the same four HST’s and arranged them these four ways and there are even more combinations, especially if you use different colored HST’s!

For this week’s block, we are going to lay everything out in a 16 square block, so it will be assembled exactly the same way as we assembled the block in week 1, except each square is made of a half square triangle!

5.  Sew together the squares.  First we will sew the top row together.

Take the first two squares and place them right sides together, paying close attention to which edge you want to sew!

Mark your 1/4″ seam allowance using your seam gauge and sew on the line.

Then take your third square and place it right sides together on top of the second square, mark your seam allowance, and sew.

Then take your fourth square, and place it right sides together with on the third square, mark your seam allowance, and sew.

You now have your top row completed!

Sew the remaining rows together in the same way.  You will then have four rows completed.

6.  Press the seams for each row.  Try to alternate the direction the seams are pressed (1st row to the right, 2nd row to the left, etc.) so they line up better later.

7.  Sew the rows together.  We will start with the top two rows. pay close attention to which edges you are wanting to sew together and tun them right sides together.  Match up the very center seam first and pin, and then try to match all the other seams as best as you can and pin them so they stay in place while you are sewing.  Mark out your 1/4″ seam allowance and sew.

Then sew on the third row – flip it right sides together on the second row (again be careful to sew the correct edges together!).  Match up the seams and pin together, mark out your seam and sew.

And do the same thing for the very last row!  Turn it right sides together on top of the third row, pin, mark your seam allowance and sew!

And your half square triangle block is now completed!!!

Next week we will be using half square triangles in a new way!  Stay tuned for next week!!!

Happy sewing!


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