Quilt sashing calculator
Twenty 12" blocks in a 4 x 5 grid with 2" sashing makes a 54" x 68" quilt center and takes about 1 yard of sashing fabric. Enter your blocks and sashing width below for every piece to cut, with or without cornerstones.
You will need
How sashing changes your quilt size
Sashing is the polite space between blocks, and it is also free real estate: every strip grows the quilt without another pieced block. The arithmetic: finished width = blocks across x block size + (blocks across - 1) x sashing width, and the same down the length. Twenty blocks that would make a 48" x 60" top become 54" x 68" with 2" sashing, which is most of the difference between a generous lap quilt and a stingy one.
Cornerstones or continuous sashing?
Without cornerstones, vertical pieces sit between blocks and long horizontal strips run the full row width: fewer seams, faster, and a quiet, unbroken lattice. With cornerstones, every sashing piece is a short identical cut and small contrasting squares sit at each intersection: more pieces, but the cornerstones act as built-in alignment marks, since each one must meet the block seams on both sides. Beginners often find the cornerstone version comes out straighter precisely because it has more checkpoints.
Keeping sashed rows aligned
The classic sashing failure is blocks that drift sideways from row to row, visible the moment you stand back. The cure is pins and pressing: press seams toward the sashing, then when joining rows with continuous strips, mark where each block seam should land on the strip and pin it there before sewing. With cornerstones, the seams nest naturally and the lattice polices itself.
Sources and methodology
All pieces cut at finished size + 1/2" for seam allowance. Without cornerstones: (columns - 1) x rows vertical pieces at sashing cut x block cut, plus (rows - 1) full width strips pieced from WOF. With cornerstones: (columns - 1) x rows vertical and columns x (rows - 1) horizontal pieces, plus (columns - 1) x (rows - 1) cornerstone squares. Yardage = WOF strips at the sashing cut width x that width / 36, rounded up to the next quarter yard, with usable width = nominal - 2". Cross-checked against published quilting references.
Sashing questions, answered
Between a quarter and a third of the block size reads as balanced: 2" to 3" finished for 9" or 12" blocks is the sweet spot. Narrower than 1 1/2" and the sashing reads as an accident; wider than half the block and the blocks start to look like postage stamps on wrapping paper. Sampler quilts with busy blocks earn wider sashing to give the eye somewhere to rest.
No, deliberately: cornerstones are nearly always a contrast fabric, and they are tiny. A 4 x 5 quilt needs just 12 cornerstone squares at 2 1/2", which is one strip of almost any scrap. The calculator reports the count and cut size so you can raid the scrap bin with confidence.
Matching the block background makes blocks float on a continuous field, very calm and modern. Contrasting sashing draws a lattice and makes each block a framed picture, the traditional sampler look. Neither is wrong; audition both by laying strips between two finished blocks before cutting the whole set.
Within reason, yes, and quilters have quietly used it this way for generations. Cut all sashing to fit your smallest block, then trim each block to match. A quarter inch of variation disappears entirely; more than that and it is kinder to re-square the blocks first. Sashing forgives; it does not perform miracles.