Patchwork Block Diagram
Zero Waste & No Sign-up: Generate cutting diagrams with automatic seam allowance for common patchwork blocks. Visualize block construction with accurate SVG diagrams.
How to Use the Patchwork Block Diagram
Pick a block pattern — four-patch, nine-patch, sixteen-patch, rail fence, or HST pinwheel — and enter the finished block size and your seam allowance. The tool draws the block as a scaled diagram with two alternating fabric placements and labels every piece with its exact cutting size, so you can see construction and cutting requirements at a glance.
Square and rectangular pieces are cut at the sub-unit's finished size plus two seam allowances. The pinwheel's half square triangle pieces get an extra 3/8 inch on top of that to survive the diagonal seam, which reproduces the classic formula at the standard quarter-inch seam: finished triangle unit plus 7/8 inch. An 8-inch four-patch therefore cuts four 4-1/2 inch squares, while an 8-inch pinwheel starts from 4-7/8 inch squares.
Below the diagram, identical pieces are grouped into a cutting summary with counts, ready to take to the cutting mat. The summary pairs naturally with the fabric yardage calculator: feed each line's piece size and count into it to turn the diagram into a shopping list for any number of blocks.
Frequently Asked Questions
Which block patterns does the diagram support?
Five classics: four-patch, nine-patch, sixteen-patch, rail fence, and the HST pinwheel. Each is drawn to scale with two alternating fabric placements and labeled with exact cutting sizes for the block size and seam allowance you set.
How are the cutting sizes in the diagram calculated?
Squares and rectangles are cut at the sub-unit's finished size plus two seam allowances. The pinwheel's half square triangle pieces add a further 3/8 inch for the diagonal seam, which reproduces the classic finished-plus-7/8 inch rule at a quarter-inch seam.
Can I use the diagram for any block size?
Yes — enter any finished size. A nine-patch divides it into thirds, a sixteen-patch into quarters, and the rail fence into four full-width strips, so sizes divisible by the grid (6, 9, or 12 inches for a nine-patch) give the tidiest cutting numbers.