How to make half-square triangles
A half-square triangle is a square made of two triangles sewn along the diagonal. For a 3" finished unit, the two-at-a-time method starts with two 3⅞" squares: the finished size plus ⅞".
All three methods below sew the bias edge before it is cut, so the triangles never stretch.
By Editorial Staff
Two at a time
Cut a light and a dark square 3⅞". Lay them right sides together with the light one on top, and draw a line corner to corner on its back.
Sew ¼" from the line on both sides.
Cut on the line.
Open each one and press the seam toward the dark fabric. Each pair makes two half-square triangles, 3½" with seam allowance, 3" when sewn into the quilt.
Eight at a time
For eight 3" units, cut a light and a dark square 7¾", twice the finished size plus 1¾". Lay them right sides together, draw both diagonals on the back of the light one, and sew ¼" from both sides of both lines.
Cut the square in half across and down through the middle, then cut each quarter on its drawn diagonal. Press open: eight half-square triangles, trimmed to 3½".
Make them big and trim to size
For the most accurate units, cut the squares 1" bigger than the finished size (4" for 3") and make them two at a time. Then lay a square ruler on each unit with its diagonal line on the seam and trim two sides; turn the unit and trim the other two to 3½".
Cut sizes for half-square triangles
| Finished | Two at a time | Eight at a time | Trim to size |
|---|---|---|---|
| 1" | 1⅞" | 3¾" | 2", trim to 1½" |
| 1½" | 2⅜" | 4¾" | 2½", trim to 2" |
| 2" | 2⅞" | 5¾" | 3", trim to 2½" |
| 2½" | 3⅜" | 6¾" | 3½", trim to 3" |
| 3" | 3⅞" | 7¾" | 4", trim to 3½" |
| 3½" | 4⅜" | 8¾" | 4½", trim to 4" |
| 4" | 4⅞" | 9¾" | 5", trim to 4½" |
| 5" | 5⅞" | 11¾" | 6", trim to 5½" |
| 6" | 6⅞" | 13¾" | 7", trim to 6½" |
The half-square triangle calculator gives the number of squares for any count, and the Half-Square Triangle quilt pattern uses them in every size.
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