Setting triangle calculator
For 12" blocks set on point, cut side triangle squares at 18 3/4" and corner squares at 9 7/8" (floated). Enter your block size and layout below for exact cutting sizes, counts, and your finished on point dimensions.
Cut
Why setting triangles have two different formulas
The whole game is keeping the straight grain of the fabric on the outside edge of the quilt, where stretch would cause waves. Side triangles get their long edge on the quilt edge, so they are cut as quarter square triangles: a big square cut twice on the diagonal puts straight grain exactly there. Corner triangles get their short edges on the quilt edge, so they are cut as half square triangles: a smaller square cut once. Different geometry, different formula, same goal of a calm, flat edge.
Setting triangle cutting chart (floated)
Common block sizes with the 1/2" float included. Each side square yields 4 triangles; each corner square yields 2, and every quilt needs exactly 4 corners.
| Finished block | Side square (cut twice) | Corner square (cut once) | Block diagonal |
|---|---|---|---|
| 6" | 10 1/4" | 5 5/8" | 8 1/2" |
| 8" | 13 1/8" | 7 1/8" | 11 3/8" |
| 9" | 14 1/2" | 7 3/4" | 12 3/4" |
| 10" | 16" | 8 1/2" | 14 1/8" |
| 12" | 18 3/4" | 9 7/8" | 17" |
| 14" | 21 5/8" | 11 3/8" | 19 3/4" |
| 16" | 24 1/2" | 12 3/4" | 22 5/8" |
How many side triangles does my quilt need?
Two per row plus two per column, minus the four spots the corners claim: side triangles = 2 x (rows + columns - 2). A 4 x 5 layout needs 14 side triangles, which is 4 squares cut twice diagonally with 2 triangles left over for the parts drawer. The calculator counts this for you and reports the spares.
Sources and methodology
Side setting squares = (finished block x 1.414) + 1 1/4"; corner squares = (finished block / 1.414) + 7/8"; both rounded up to the next 1/8", with an optional 1/2" added to float. Side triangles needed = 2 x (rows + columns - 2); corners are always 4. On point quilt center = columns x block diagonal by rows x block diagonal, where the diagonal = finished block x 1.414. These are the standard published on point formulas, cross-checked against multiple quilting references.
On point questions, answered
Cutting the setting triangles slightly oversize so a sliver of background shows between your block points and the quilt edge. The points appear to float rather than touching the binding. Besides looking elegant, it means the binding seam cannot eat your points, which is why nearly everyone cuts oversize on purpose.
Turning a square 45 degrees makes it occupy its diagonal, which is 1.414 times its side. Twelve inch blocks set straight make a 48" wide four block row; on point, the same four blocks span almost 68". On point settings are the cheapest way to grow a quilt: same blocks, 41% more bed coverage.
You can, and the quilt will go together, but the side triangles will have bias on the outer edge of the quilt, which stretches as you handle and bind it. Wavy edges on an otherwise lovely quilt are usually this exact shortcut. The two-formula approach exists to spare you that.
Yes, sashed on point quilts are classic, but the triangle sizes change because the repeating unit becomes block + sashing rather than the block alone. Add your finished sashing width to your finished block size and enter that total as the block size above; the triangles will fit the sashed grid.