How To Sew Great Half Square Triangles


Discusses half square triangles (HSTs) and how to sew them correctly using these great tricks.

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How To Sew Great Half Square Triangles

One of the first blocks new quilters tackle are half square triangles, or HSTs. They are the next step in beginning quilting, and one of the most common blocks you will find in quilts, whether it be modern, traditional, or art! Knowing how to sew a great HST is very important, and a little more difficult than it seems! But the best part is that with these little tricks, you can make great HSTs! How to make a HST:

How To Sew Great Half Square Triangles


  1. What size are you going to make the block? You must choose, but choose wisely. Where as the right block can give you great HSTs, the wrong size can take it from you….;) (Indiana Jones and the last quilt top…) Example: one method has you make an hour glass block from which you can make HSTs. Two squares of contrasting values can give you eight HSTs (a real time saver for lots of HSTs). Another method will use two squares of contrasting value to yield two hst blocks.
  2. With the lighter block you will draw a diagonal line on the wrong side of the fabric from one corner to the other, then turn the block 180 degress and make another diagonal line from the corner to the opposite corner. You should have a large X on the back of your block.
  3. Place the lighter block on the contrasting block, and sew a quarter inch from each of the lines on both sides. It’ll look like an outlined X.
  4. Cut the block along the drawn lines, and press the seam to the darker fabric side.


Half Square Triangles


You have now made eight HSTs!

To get the prefect HST that has oops room, you need to do a bit of math… I know, just great isn’t it… Well, don’t get too down hearted, because there are some magic numbers to remember for your calculations.

Example: if you want to make a finished block the size of 8 inches, we calculate the finished size 8 inches plus 7/8th inch to make HSTs.

To make HSTs with oops room, add another ½ in to your block size, then when you have finished sewing your HST block you can square it up to the size you require for your quilt (this method only makes two half square triangles).

When using the hour glass block to make HSTs, use this calculation:

Finished size + 7/8 x 2+ 2 1/8 + ½= size square you need to cut (including oops room).

Example: in the picture above my finished block is 5 in. 5+ 7/8= 5 7/8 x2= 11 ¾ +2 1/8= 13 7/8 +1/2= 14 3/8. I need to cut two fabrics of contrasting values to 14 3/8 inches square. This will yield the size of the HST I want. This formula will size any block you want.

When following a pattern, they don’t always include oops room. If you want to work the pattern as written, go for it. If you want to include oops room, you need to find out which fabric cut will be the HST, and add a ½ in to the cutting requirements. Example: the two HST method below:


Half Square Triangles


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The basic unit of a quilt top, usually square but can be rectangular or other shapes. Blocks can be pieced, appliqued or plain.
Finished Size
The final sewn measurement or dimensions of a completed block without seam allowances. Thus a 6" sewn measurement block would be cut 6.5" to allow for 1/4" seam allowances.
Method of using an iron to press seams and blocks. This means simply pressing downwards on the seam with the iron from above and not moving the iron back and forth which can distort the block or seam.
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