Loading…
Loading…
Calculator
Cut sizes for side and corner setting triangles on an on-point (diagonal set) quilt, plus how many of each you need for your layout.
A 3 × 4 on-point set of 12″ blocks needs 10 side triangles and 4 corner triangles.
That layout takes 18 blocks (3 × 4 in the full rows plus the offset rows between) and the pieced top comes out about 50⅞″ × 67⅞″ before borders, with no sashing. Both triangle cuts are a touch generous — trim the edges straight after the rows are joined.
| Piece | Cut | Squares | Per fat quarter | Fat quarters | Yardage |
|---|---|---|---|---|---|
| Side triangles | 18¼″ squares (cut X) | 3 | — | — | 1¼ yd (2 strips) |
| Corner triangles | 9⅜″ squares (cut once) | 2 | 2 | 1 | ½ yd (1 strip) |
About 1¾ yd of one fabric covers both, cut as separate strips. Yardage assumes 40″ usable width; fat quarters assume 18″ × 21″ after trimming.
Free. No trial, no subscription, no account needed — ever. Save results on this device, or sign in to keep them on every device.
| Finished Block | Side Triangle (cut, X) | Corner Triangle (cut, ↘) |
|---|---|---|
| 6″ | 9-3/4" | 5-1/8" |
| 8″ | 12-5/8" | 6-5/8" |
| 9″ | 14" | 7-1/4" |
| 10″ | 15-1/2" | 8" |
| 12″ | 18-1/4" | 9-3/8" |
| 14″ | 21-1/8" | 10-7/8" |
| 15″ | 22-1/2" | 11-1/2" |
| 16″ | 24" | 12-1/4" |
| 18″ | 26-3/4" | 13-5/8" |
Side triangle squares are cut with two diagonal cuts (an X) — 4 triangles per square. Corner triangle squares are cut with one diagonal cut — 2 triangles per square.
| On-Point Grid (rows × cols) | Side Triangles | Corner Triangles |
|---|---|---|
| 3×4 | 10 | 4 |
| 4×5 | 14 | 4 |
| 5×7 | 20 | 4 |
| 6×8 | 24 | 4 |
| 7×8 | 26 | 4 |
Formula: side triangles = 2 × (rows + cols) − 4. Corner triangles = 4, always.
An on-point (diagonal set) layout rotates every block 45°, so the rows run corner-to-corner instead of edge-to-edge. That leaves triangular gaps around the outside of the grid — side setting triangles fill the gaps along the edges, and corner setting triangles fill the four corners.
Both are deliberately cut oversized and trimmed after piecing, for two reasons: it's much easier to trim a slightly-too-big triangle flush than to stretch a slightly-too-small one, and cutting them as quarter-square (side) or half-square (corner) triangles keeps the straight grain running along the quilt's outer edge instead of the stretchier bias grain — a bias outer edge ripples and stretches out of shape over time.
A background solid or low-volume print is the most common choice — it lets the on-point blocks read as the focal point.
We may earn a commission on purchases made through these links, at no extra cost to you. Learn more.
Side setting triangles are cut oversized so the outer edge falls on the straight grain: square size = (finished block size × 1.414) + 1.25", cut with two diagonal cuts (an X) to yield 4 triangles per square. For a 12" block, that's an 18-1/4" square.
Corner setting triangles are cut as half-square triangles: square size = (finished block size ÷ 1.414) + 0.875", cut once diagonally to yield 2 triangles per square. For a 12" block, that's a 9-3/8" square. You always need exactly 4 corner triangles, regardless of quilt size.
For an on-point grid of R rows × C columns of blocks: side triangles needed = 2×(R+C)−4, and corner triangles needed = 4 (always). A 5×7 on-point grid needs 20 side triangles and 4 corner triangles.
Both methods are chosen so the triangle's outer edge (the one that becomes the quilt's outer edge) falls on the fabric's straight grain instead of the stretchier bias grain. A quarter-square cut (X, 4 triangles) puts the straight grain on the long outer edge for side triangles; a half-square cut (1 diagonal, 2 triangles) does the same for corner triangles.