How to make half square triangles using a grid video tutorial

Half square triangles (HST) are basic shapes in quilting. You can make full quilts using just HSTs.

They can be made with different techniques: the traditional two at a time, 8 at a time, and my favourite and flexible way to make any amount of HSTs you like at once.

Today’s video demonstrates how to make HSTs using a grid.

For today’s block we need 12 HSTs so I made a grid 2 H x 3 W. This translates to 2 x 4″ = 8″ and 3 x 4″ = 12″.

So cut 2 pieces 8″ x 12″ in contrasting fabrics and get going! I added 1/2″ to each measure – I prefer trimming than being short.

Finished HST size: 3 1/2″ x 3 1/2″

Starting squares: 4″ x 4″

How to calculate the size of the grid

To make HSTs in bulk you need to use the Two HSTs at a time chart below to calculate the size of the grid you need.

Select the finished size of your HST, eg 3 1/2″ x 3 1/2″.

The starting square for a finished 3 1/2″ x 3 1/2″ HST is 4″ x 4″.

Using 4″ x 4″ as the starting size and the number of HSTs you need you can calculate the grid size.

Let’s say you need 36 half square triangles.

Each 4″ x 4″ square makes 2 HSTs, therefore you need a grid with 18 squares (36 divided by 2).

Using the multiplication tables you can work out how many rows and columns you need to make a grid with 18 squares.

In this case I can think of 2 grids to get 18 squares:

Grid illustration

  • Option A: 3 squares x 6 squares, or
  • Option B: 2 squares x 9 squares

Tip: On the site Research maniacs you can enter any number to see which combinations of two numbers multiplied will equal that number.

Now that you know the grid you need to obtain 36 HSTs you need to work out the size of the 2 fabric panels.

How to calculate the size of the fabric panels

Multiply your starting square (4″) by the grid height (3): 3 x 4″ = 12″

Then multiply the starting square (4″) by the grid width (6): 6 x 4″ = 24″, so your 2 panels will be 12″ x 24″.

The other option requires 4″ x 2 = 8″ and 9″ x 4″ = 36″, so your 2 panels will be 8″ x 36″.

This method is very accurate but you may choose to add 1/4″ to the panels.

Two HSTs at a time reference chart

Finished HST sizeStarting square
2 1/2″3″
3″3 1/2″
3 1/2″4″
4″4 1/2″
4 1/2″5″
5″5 1/2″
5 1/2″6″
6″6 1/2″
6 1/2″7″
7″7 1/2″
7 1/2″8″
8″8 1/2″
8 1/2″9″
9″9 1/2″
9 1/2″10″
10″10 1/2″
10 1/2″11″
11″11 1/2″
11 1/2″12″
12″12 1/2″
Two half square triangles at once table

My book Turnabout Patchwork

“Turnabout Patchwork. Simple quilts with a twist” is all about playing with blocks – making a block, slicing it up, and turning or repositioning the pieces to make a completely different block (sometimes two smaller blocks) to yield endless quilt tops.

See all the quilts in the book in a real life project

Do you wish to receive my tutorials in your inbox?

Share your work!

If you make any of my tutorials this is how you can share your pictures:

  • On Instagram please tag me with @teresadownunder and hashtag #teresadownunder
  • Join my Facebook group and post your pictures there
Ribbon star quilt block


  1. Hi Therese

    I used your Youtube video to make the Diamond Attic Window cushion, which was very good to have seen prior to making it.

    I have attached a photograph.

    Cheers and thanks


    Liked by 1 person

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: