On-point quilt calculator

Free. No subscription. No email.

Enter your finished block size and layout to get the setting and corner triangle squares to cut, how many blocks and triangles you need, and the size of the quilt.

InchesCentimetres

Finished block size

Blocks across the top

Blocks down the side

CuttingExact sizeSlightly bigger to trim

Round up to

Calculate

Worked example

Questions

What size do I cut setting triangles?

For the side (setting) triangles, multiply the finished block size by 1.414 and add 1¼", then round up to the next ⅛". Cut that square on both diagonals to get four triangles. A 12" block needs 18¼" squares.

What size do I cut corner triangles?

Divide the finished block size by 1.414 and add ⅞", then round up to the next ⅛". Cut two squares once on the diagonal to get the four corners. A 12" block needs 9⅜" squares.

Why are side triangles cut from a quarter-square?

Cutting a square on both diagonals puts the straight grain along the long outer edge of each triangle, so the edge of the quilt doesn't stretch. Corner triangles are cut once so their straight grain runs along the two outer edges.

How many setting triangles do I need?

For a layout measured as blocks across the top and blocks down the side, you need 2 × (across − 1) + 2 × (down − 1) side triangles and always 4 corner triangles. A 3 × 4 layout needs 10 side triangles, from 3 squares with 2 to spare.

How big will my on-point quilt be?

Each block measures its diagonal on point: the finished size × 1.414. Three 12" blocks across make a 50.9" wide centre, before borders.

Should I cut setting triangles bigger?

Some quilters cut them slightly larger so the blocks "float" and trim the edges afterwards. The "slightly bigger" option adds ⅛" to each square, which matches patterns that round up generously.

Assumes ¼" seams (0.75cm in metric) and 40" usable fabric width (102cm). Cut sizes match Quiltville and Christa Quilts; triangle and block counts are checked against a model of the layout.