The half square triangle is one of the most basic quilting blocks.  You make this square over and over as you make stars and other quilt blocks.

This is a great block to use up small pieces of fabric.  You can make these blocks in any size you want.  Almost all quilters have several techniques that they use to make these blocks. 

It is easiest to make half square triangles from squares.  If you cut triangles, you may stretch the bias.  Since this is a scrappy quilting site, we will just make 2 blocks at a time.

First determine the size of the square you want.  Let's make our block to finish at 5 inches.  To make the block you need two contrasting pieces of fabric, such as a light and a dark, or a medium and a dark.  Cut the squares the size you want them to finish, plus 7/8 of an inch.

The picture to the left shows the back two quilt squares.  Put the pieces right sides together, and draw a diagonal line across one of the squares on the back.  It is usually easier to see the line if you make it on the light fabric. Sew the 1/4 inch seam allowance on each side of the line.  Then cut down the drawn diagonal line and you will have 2 half square triangles.  Press to the darker side of the block.

 

 

There are many ways to arrange these blocks.  One of the most popular is the Pinwheel Block.

To the left is just one example of a half square triangle layout, in addition to the Pinwheel and the layout at the top of the page.  Notice how all the lights are turned toward the center in the block at the left.  You could do the same thing with the darks also.

 

Since if it so easy to square these blocks up, a lot of people oversize the squares they cut for these blocks, and then just trim them after the are sewn and cut so they will be perfectly square.