This is a quick tutorial on making Half-Square Triangle Blocks –
HST for short.
Exact: The traditional “exact” formula for cutting a square to make a Half-Square Triangle Block is: Finished size + 7/8″.
For example, if your HST is supposed to be 2″ finished; cut the square 2-7/8″.
Oversized: If you prefer to make the HST units larger and then trim them to size, add 1″ to the finished size.
The units will be a little bigger than they need to be and you trim them down to the right size. This has become my favorite method.
Here we go….
Method 1: Sew Before You Cut
Draw a line from corner to corner on lighter fabric.
Sew a scant 1/4″ from both sides of the line. Scant means just a thread less than a full 1/4″.
Cut apart on drawn line to get two HST blocks! Press to the darker fabric and trim to size as needed.
Method 2: No Math Method
1. If you are using 3″ squares to make a block like this one and need to make an HST that will fit, simply use two 3″ squares; a light and a dark.
2. Place fabrics right sides together and draw a line from corner to corner on the lighter fabric.
3. Draw a SECOND line 1/2″ away – this will give you a bonus HST that is 1″ smaller than the large HST.
4. Sew ON THE LINES, actually just a hair inside would be even better.
5. Cut apart between sewn lines and press to the darker fabric.
6. The large HST will fit perfectly with the plain 3″ squares in the four patch block above.
7. The BONUS block can be squared up to 2″ and saved for a scrappy project.
Taking this one step further (and better!), there is a tool that was created just for this method!
The Folded Corner Clipper makes Half square Triangle blocks by allowing you to trim the corner first. You can use it for lots of other units too. Here’s a LINK to a video with instructions on how to use it.
