Half-Square Triangle Unit Techniques

Half-square triangles are a basic unit of quilting used in many blocks or on their own. 

Here are two different ways to make this simple unit. While the same-size-square technique is more common, faster and easy to accomplish, the trim-to-true technique will give you a more accurate unit.

Same-Size-Square Technique

This construction method works with two same-size, different-color squares and will yield two half-square triangle units.

1. Cut two squares from different colors, adding 7/8" to the desired finished size. For example, for a 3" finished half-square unit, cut 3 7/8" squares.

2. Using a ruler, draw a diagonal line from corner to corner on the wrong side of the lightest color square. Layer the squares right sides together. Stitch 1/4" on either side of the drawn line (Figure A).

3. Cut the squares apart on the drawn line, leaving a 1/4" seam allowance on each side, making two triangle units, referring to Figure B.

4. Open the triangle units and, on the wrong side of the fabric, press seam allowances toward the darker fabric, making two half-square triangle units (Figure C). 

Trim-to-True Technique

This half-square triangle construction method allows for quick cutting of squares, reinforced diagonal seams and rotary-trimmed units for absolute accuracy. This method for creating the units is the same as the same-size-square technique, but by starting with oversize squares, exact accuracy can be obtained when they are trimmed. Always cut and stitch a sample before cutting all your units.

1. To determine the size square needed for the desired size of your half-square triangle unit, add 1 1/4" to the finished square size desired for trimming ease.

2. Cut the size squares determined in the previous step from light and dark fabrics to compose the half-square triangle units. Remember that each square yields two half-square triangle units. The required number of cut squares from each fabric is only half the final unit tally. Note: You can layer the two fabrics with right sides together when cutting to reduce handling of individual layers.