On-Point Quilt Calculator
Set your blocks on point and the quilt grows diagonally. Enter the finished block size and the number of blocks across and down to get the finished quilt size plus the setting triangle cuts.
Tip: use URL parameters to pre-fill, e.g. ?blockSize=12&blocksAcross=5&blocksDown=6.
The diagonal math
A block set on point uses its diagonal instead of its width. A 12-inch block has a diagonal of about 17 inches (12 × 1.414). The quilt width is the diagonal times the blocks across, plus the two corner triangle allowances; the height works the same way with the blocks down. The calculator adds 1/4-inch seams throughout.
Setting triangles
Side setting triangles fill the jagged edges between blocks. Cut a square at the block diagonal plus 1.25 inches, then cut it on both diagonals to make four triangles. A 12-inch block needs 17 + 1.25 = 18.25-inch squares. You need 2 × (across + down) of these triangles, which is 22 for a 5×6 layout.
Corner triangles fill the four corners. Cut a square at half the block diagonal plus 0.875 inches (about 8.9 inches for a 12-inch block), then cut it once on the diagonal. Two squares make the four corner triangles.
What each input means
Finished block size: the visible block size after seaming, from your pattern.
Blocks across / down: the grid of full blocks in your layout, not counting the setting triangles. A 5 across by 6 down layout uses 30 full blocks plus 22 side triangles and 4 corners.
Common questions
Do I need sashing for an on-point quilt?
No — sashing is optional. This calculator assumes blocks touch, with only setting triangles filling the edges. Add sashing strips as a separate step if your pattern uses them.
Why does my block look smaller on point?
On-point blocks appear smaller visually because the diagonal is shorter than the block's width plus its neighbor's. That's the trade-off that makes the layout dynamic.
Can I mix block sizes?
This calculator assumes one uniform block size. For mixed sizes, calculate each section separately and add the widths by hand.
Where does 1.414 come from?
It's the square root of 2 — the ratio between a square's side and its diagonal. It appears whenever you set square blocks on point.