On-Point Quilt Setting Triangle Calculator
Setting blocks on point turns the square blocks 45 degrees. The gaps along the edges are filled with larger side triangles and smaller corner triangles. Enter the finished block size to calculate the square cut sizes used to make those triangles.
Square sizes for the two triangle types
For a finished square block size B:
- Side setting triangles: cut a square of
B × √2 + 1¼ in, then cut it diagonally twice to make four triangles. - Corner setting triangles: cut a square of
B ÷ √2 + ⅞ in, then cut it diagonally once to make two triangles.
| Finished block | Side-triangle square | Corner-triangle square |
|---|---|---|
| 4 in | 6.91 in | 3.70 in |
| 6 in | 9.74 in | 5.12 in |
| 8 in | 12.56 in | 6.53 in |
| 10 in | 15.39 in | 7.95 in |
The calculator keeps the decimal result so you can choose a cut size that matches your ruler and pattern. If you round to a convenient fraction, round up and square the sewn setting units to the dimensions your pattern requires. Counts depend on the number of blocks in each row and the layout, so this page calculates cut sizes rather than assuming a particular quilt grid.
Estimate a row span
A single square block rotated 45 degrees spans B × √2 from corner to corner. A row of N blocks therefore has a nominal span of N × B × √2, before edge trimming. Use your pattern's layout diagram to count the triangles and confirm the finished edge before cutting; the calculator gives starting cut sizes and a nominal row span, not a complete quilt layout.
Source
- Triangle cut sizes use the geometry described above: √2 for the 45-degree diagonal and the stated ¼ in seam allowance.