Open Setting triangles in the studio. The form on this page is that calculator.
Why side triangles and corner triangles are cut differently
On-point blocks sit on their corners, and the gaps at the edge of the quilt are filled with setting triangles. The outside edge of the quilt should be on the straight grain, or it stretches while you quilt it and the border ripples.
Side triangles are cut from a square sliced on both diagonals, so each triangle's long edge is on the straight grain. Corner triangles are cut from a square sliced once, for the same reason. Cutting every setting triangle the same way puts the bias on the outside of the quilt.
How the setting squares are calculated
The side square is the block's diagonal plus 1 1/4 inches. The corner square is half that diagonal plus 7/8 inch. Both are rounded up to the next eighth, which is a size you can find on a ruler. Cut them a thread larger still if you like to trim after the quilt top is together. Do not cut them smaller.
- Side triangles = two for every row and every column, except the four corners
- Side squares = those triangles ÷ 4, rounded up. Each square gives four side triangles.
- Corner squares = two. Each is cut once, for four corner triangles.
A single block on point needs only the four corners. The finished size on the card is the blocks only. Sashing and borders are extra. Add them with the quilt size calculator once you know the on-point measurement. Quarter-square blocks that are meant to be hourglasses use the hourglass calculator instead.
Setting triangles for a 3 by 3 grid
Every row is a 3 by 3 of the same block, which needs 8 side triangles (2 squares) and 4 corner triangles (2 squares). Larger grids need more side squares. The corner count stays at two squares.
| Finished block | Side square | Corner square | On-point size, 3 × 3 |
|---|---|---|---|
| 4 in | 7 in | 3 3/4 in | 17 × 17 in |
| 6 in | 9 3/4 in | 5 1/8 in | 25 1/2 × 25 1/2 in |
| 8 in | 12 5/8 in | 6 5/8 in | 34 × 34 in |
| 10 in | 15 1/2 in | 8 in | 42 3/8 × 42 3/8 in |
| 12 in | 18 1/4 in | 9 3/8 in | 50 7/8 × 50 7/8 in |
How to use this calculator
- Enter the finished block, the size it is after piecing, not the size of the squares inside it.
- Enter the columns and rows of the on-point grid. A 3 by 3 is nine blocks.
- Cut the side squares and slice each one on both diagonals. Cut the corner squares and slice each one once.
- Sew the triangles on, then trim the quilt edge if you cut them a thread large. The straight grain should be the outside edge.
Tips for on-point sets
- Count the side triangles before you cut. A 3 by 3 needs eight. A 4 by 5 needs fourteen. The card does that count.
- This chart has no sashing. Sashing changes the size the triangles have to fill. Add sashing in the layout first, or treat the block-plus-sash as the block size only if the pattern tells you to.
- Press toward the setting triangles when you can, so the block's seams sit flat under them.
When the piece is part of a whole quilt. On-point layouts in the studio still use these two cuts for the edge. The fabric calculator counts every piece in a design, then adds binding, backing, and batting. These pages answer one question at a time.