Precision Quilt Piecing Part 3: Quarter & Triple Triangle Squares

Heads up! This article is part of a series on precision quilt piecing techniques. Make sure to read the previous installment of this series here.

The most accurate and efficient method for piecing quarter and triple triangle squares is to make them from a half-square triangle. Other techniques for piecing these units involve cutting and sewing individual pieces or having finished units with bias edges. The first method is less efficient and the second is less accurate. Follow along as I take you through the precision technique basics of piecing quarter and triple triangle squares.

Crunching the Numbers

To make the half square triangle you will need to cut your squares 1½” larger than the finished size of the quarter/triple triangle square. For example, if the finished size of the quarter/triangle square is to be 2”, cut the squares for your half square triangle 3½”.

Proceed to make half-square triangles from two contrasting 3½” squares. See Part 2 of this series for more on half-square triangles.

Piecing It Together

quarter triangle squares 1 Quarter Triangle

Step 1: To make the quarter-triangle square, position the two half-square triangles right sides together, with the colors opposing of each other. Align the seams, nesting them together, and draw a diagonal line from corner to corner across the half-square triangle.

quarter triangle squares 2 Step 2: Stitch a scant ¼” along both sides of the drawn line then cut along the drawn line and press open. You will have two quarter-triangle squares.

quarter triangle squares 3 Step 3: To trim, center the cross hatches of the Precision Trimmer 6 ruler at the center of the quarter-triangle square making sure that the diagonal lines line up. Trim two sides. Turn the quarter-triangle square around and reposition the Precision Trimmer 6 making sure that all lines match up. Trim the other two sides.

triple triangle squares 1 Triple Triangle

Step 1: To make a 2” finished triple triangle square, cut three squares 3½”. Make half-square triangles from two of the fabrics.

triple triangle squares 2 Step 2: On the wrong side of the half-square triangle mark a diagonal line from corner to corner crossing the stitching line.

triple triangle squares 3 Step 3: Center one of the half-square triangles on the third 3½” square, right sides together.

triple triangle squares 4 Step 4: Stitch a scant ¼” along both sides of the drawn line then cut along the drawn line and press open. You will have two triple triangle squares.

triple triangle squares 5Step 5: To trim, center the cross hatches of the Precision Trimmer 6 ruler at the center of the triple triangle square aligning the diagonal lines. Trim two sides. Turn the unit around, re-align and trim the other two sides to finish off your new triangles!

See you next time when we will discuss flying geese units in the next installment of this series.

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9 Responses to “Precision Quilt Piecing Part 3: Quarter & Triple Triangle Squares”

  1. Mary Green

    I just recently sewed qtr sq triangle for a BOM and hadn’t realized how easy they were to make. Good directions here.

    Reply
  2. Laurilli J Bazille

    Is there a printer friendly way to print these directions? thanks,it really like the clear instructions.

    Reply
  3. Adrian

    If I wanted to make my HSTs to use to make quarter square triangles in your 8 at a time method and I wanted my finished quarter square triangles to be 4″, how big would I need to cut the square to make the 8 at a time HSTs? I simply cannot wrap my head around that math. Help!

    Reply
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      Hello Adrian,

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  4. Malissa Rivoire

    How do you calculate the beginning size of fabric to make an 8.5″ half square triangle block

    Reply
    • Customer Service

      Hi Malissa,
      Thanks for contacting National Quilters Circle with your question. First to clarify, you are making half square triangles (HST) using two squares of fabric and you want them to measure 8-1/2″ which in turn means they will be 8″ finished in the quilt? This would mean cutting 8-7/8″ squares. Then drawing a diagonal line from corner to corner and stitching 1/4″ away from each side of the line. Cutting down on the marked line and pressing them open you would have 2 matching HST. Some quilters prefer cutting those first squares up to the whole inch – in this case 9″ and then trimming after the last pressing step. Your formula is this: take the size you want the unit to be “finished” in the quilt (all seam allowances removed) and add 7/8″. That is your starting point. Many like I said will just add 1″ which allows for just a tiny trim of each HST to make it exact.
      Happy Quilting
      Colleen
      National Quilters Circle

      Reply