Printable half square triangle chart

For each finished size printed here, cut two starting squares ⅞″ bigger than the finished unit, sew, and subcut on the diagonal. The table below works that rule — and the four- and eight-at-a-time variants — through 13 finished sizes, every value computed by Quilt Block Atlas, ready to print.

The chart — 1″ to 8″ finished

The three method columns are the size to CUT. Finished size is the unit after it is sewn in; Trim to is what the sewn unit should measure before its outer seams — the finished size plus ½″. Two- and eight-at-a-time starting squares are exact. Four-at-a-time is the rounded-and-trimmed method: its starting square is rounded up to the next ⅛″, and each unit is trimmed to the Trim to column.

Half square triangle starting squares by finished size and method
Finished size	Trim to	Two at a time	Four at a time	Eight at a time
1″	1½″	1⅞″	2⅝″	3¾″
1½″	2″	2⅜″	3⅜″	4¾″
2″	2½″	2⅞″	4⅛″	5¾″
2½″	3″	3⅜″	4¾″	6¾″
3″	3½″	3⅞″	5½″	7¾″
3½″	4″	4⅜″	6¼″	8¾″
4″	4½″	4⅞″	6⅞″	9¾″
4½″	5″	5⅜″	7⅝″	10¾″
5″	5½″	5⅞″	8⅜″	11¾″
5½″	6″	6⅜″	9″	12¾″
6″	6½″	6⅞″	9¾″	13¾″
7″	7½″	7⅞″	11⅛″	15¾″
8″	8½″	8⅞″	12⅝″	17¾″

Scroll sideways to see every method.

Which column to use

Scroll sideways to inspect every label.

One 3″ half square triangle worked through: finished size, trim target, starting squares.

A 3″ finished half square triangle is trimmed to 3½″ before its surrounding seams, and starts as two 3⅞″ squares — the finished size plus ½″ for the edge seams and ⅜″ so the allowance survives the diagonal cut.

Two at a time: cut 2 squares from the Two at a time column beside your finished size, sew a seam each side of the drawn diagonal, subcut on it once, and get 2 exact units. This starting square is exact; the Eight at a time starting square is exact too.

Four at a time: cut 2 squares, sew around the perimeter, cut both diagonals, and get 4 units with bias outer edges. The starting square is rounded up, so every unit is trimmed to the Trim to column — plan on the extra pass.

Eight at a time: cut 2 larger squares, sew a seam each side of both drawn diagonals, cut on both diagonals and twice through the middle, and get 8 matching units from an exact starting square — the batch method for a block that repeats one unit. For an accepted ruler-compatible size this chart does not print, the half square triangle calculator accepts positive ⅛″-increment finished sizes within its supported calculation range and blanks any method whose starting square exceeds usable fabric width.

Blocks these squares build

11 blocks in this library are pieced from half square triangles, each with its own chart at accepted ruler-compatible sizes.

Print this chart at 100%

Press Ctrl+P (⌘P on a Mac) and choose "Actual size" or 100% — never "Fit to page". Then measure this square: it must be exactly 1″. If it is not, the whole sheet is scaled and every number on it is wrong — printing quilt patterns at 100% walks through the settings.

Common questions

Why add ⅞ inch and not just ½ inch?

½″ covers the seam allowance on the edges, and the remaining ⅜″ survives the diagonal cut — a diagonal seam consumes more than a straight one. Cut only ½″ bigger and every unit finishes small, which is the most common HST complaint there is.

Can I cut the squares bigger and trim them down?

Yes — cutting oversize and trimming down is widely taught, and the published amounts differ by source; how to square up a quilt block carries the attributed range. The trim target is the Trim to column: a 3″ finished unit is trimmed at 3½″, never at 3″. Oversizing costs fabric and a trimming pass; the chart's exact numbers cost accuracy at the seam instead. Both work — pick one and be consistent.

How do I print this chart at actual size?

"Actual size" or 100%, never "Fit to page" — then measure the calibration square above with a real ruler before cutting anything. The setting is what you asked for; the square is what you got.

My finished size is not on the chart — where do I get it?

The half square triangle calculator computes the same three methods for accepted ruler-compatible sizes within its supported calculation range. Methods wider than usable fabric are blanked, and every block page's own chart recomputes as you type.