Squaring Up a Half Square Triangle Quilt Block

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March 5, 2014

Fabric square and ruler.The half square triangle (HST) block is very popular and is used in many patchwork quilts. When making this block it is a good idea to make them slightly oversized and then cut them down to their unfinished dimensions. This method takes a bit longer, but helps to produce uniformly sized squares. In this example the blocks were very close to desired size and just needed squaring.


If one thing is true in quilting, it is that squaring up your blocks is an important step to ensure having a square top to work with.

Total Time: 1 minute or less per block


  • rotary cutter
  • self healing cutting mat
  • square quilt template/non slip ruler, at least the size of your unfinished block (including seam allowance)


  1. On your cutting mat line up the top and and right edges of the ruler on the half square triangle (HST) block, there will be some amount of fabric extending beyond the edge of the ruler. The 45 degree line on the ruler needs to be directly over the diagonal seam.
  2. Before trimming these two seams (top and right) make sure that the other two sides of your block extend beyond the finished trimmed size. Now trim the first two sides. Make sure that neither the ruler nor the fabric slips while using your rotary cutter to trim.
  3. Trimming right side.
    Trimming top.

  4. Rotate the block 180 degrees to the left and trim the remaining two sides in the same way. For this cut you can line up the trimmed edges on the marks for your unfinished block size. For example, I squared up these blocks to 3 inches (the unfinished size). The final size will be 2.5 inches after taking a .25 inch seam, when piecing.
  5. Trimming new right after 180 turn.
    Trimming final side, new top after 180 turn.
  6. This final photo shows a before and after comparison of the squared (on the right) and unsquared (on the left) blocks. These blocks were close to their desired size to begin with and did not need much trimming.

Your block should now be the exact size you need. If you didn't cut them off earlier, the dog ears have been removed and the seam is a perfect 45 degrees.

Comparison blocks.

Here is a link to making a half square triangle block: Making Half Square Triangle Quilt Blocks

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