Guide
Half-square triangle size chart
For half-square triangles made two at a time, cut squares the finished size plus ⅞″. A 3″ finished HST needs 3⅞″ squares. If you like to trim units to size, add 1″ instead (4″ squares for a 3″ HST) and trim each unit to 3½″.
HST chart
| Finished HST | Unfinished unit | 2 at a time (+⅞″) | 2 at a time, trim (+1″) | 8 at a time |
|---|---|---|---|---|
| 1″ | 1½″ | 1⅞″ | 2″ | 3¾″ |
| 1½″ | 2″ | 2⅜″ | 2½″ | 4¾″ |
| 2″ | 2½″ | 2⅞″ | 3″ | 5¾″ |
| 2½″ | 3″ | 3⅜″ | 3½″ | 6¾″ |
| 3″ | 3½″ | 3⅞″ | 4″ | 7¾″ |
| 3½″ | 4″ | 4⅜″ | 4½″ | 8¾″ |
| 4″ | 4½″ | 4⅞″ | 5″ | 9¾″ |
| 4½″ | 5″ | 5⅜″ | 5½″ | 10¾″ |
| 5″ | 5½″ | 5⅞″ | 6″ | 11¾″ |
| 6″ | 6½″ | 6⅞″ | 7″ | 13¾″ |
Eight at a time: put two squares right sides together, sew ¼″ from both diagonals, then cut across the middle both ways and along both diagonals. Each pair of squares gives eight HSTs, so it’s quick for pinwheels and zigzags.
Quarter-square triangles and flying geese
| Finished size | QST: cut squares (+1¼″) | Flying geese size | Geese: 1 big square | Geese: 4 small squares |
|---|---|---|---|---|
| 2″ | 3¼″ | 2″ × 1″ | 3¼″ | 1⅞″ |
| 3″ | 4¼″ | 3″ × 1½″ | 4¼″ | 2⅜″ |
| 4″ | 5¼″ | 4″ × 2″ | 5¼″ | 2⅞″ |
| 6″ | 7¼″ | 6″ × 3″ | 7¼″ | 3⅞″ |
The designer counts every HST in your quilt, pairs the squares and adds them to the cutting list, so you cut exactly what you need.
Questions
Why 7/8″?
Half an inch covers the two ¼″ seams. The extra ⅜″ is what the diagonal seam takes: a ¼″ seam measured across a diagonal uses about 0.35″ more of the square.
Should I add 1″ and trim?
If your triangles come out small or wonky, yes. You use a little more fabric and spend a minute per unit trimming, and every unit comes out the exact size.
What about quarter-square triangles?
Cut squares the finished size plus 1¼″ and cut them twice on the diagonal. For an hourglass unit made from two HSTs, add 1¼″ too, or 1½″ to trim.
Updated November 9, 2026