A QuiltPlan piecing reference
Half-Square Triangles
the two-at-a-time method, start to finish
A half-square triangle (HST) is a square split into two triangles on the diagonal: the building block behind pinwheels, hourglass units, and dozens of traditional blocks. This is the classic method: one pair of squares, one seam, two HSTs.
Cut your starting squares 1″ larger than the HST's finished size.
1 · Mark
Layer two squares right sides together. Draw a diagonal line corner to corner on the top square.
2 · Sew
Sew a scant ¼″ seam on both sides of the line.
3 · Cut & press
Cut apart on the line. Press the seam toward the dark fabric.
| Finished | Cut squares | Trim to |
|---|---|---|
| 2″ | 3″ | 2½″ |
| 2½″ | 3½″ | 3″ |
| 3″ | 4″ | 3½″ |
| 3½″ | 4½″ | 4″ |
| Finished | Cut squares | Trim to |
|---|---|---|
| 4″ | 5″ | 4½″ |
| 4½″ | 5½″ | 5″ |
| 5″ | 6″ | 5½″ |
| 5½″ | 6½″ | 6″ |
Squaring up: line up the 45° line
The ruler's own 45° line runs corner to corner of the ruler. Match it to the sewn seam with one ruler corner anchored in a corner of the block, then trim the two edges that stick out past the ruler. Rotate the block, realign the 45° line the same way, and trim the remaining two edges to your unfinished size.
Need eight from one pair instead of two? See the Magic 8 method.
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