Sashing frames every block and grows the quilt as it goes. From your block grid and sashing width, you get the strips to cut, with cornerstones or without, the yardage, and the quilt size the sashing builds.
Your Blocks and Sashing
Sashing Fabric
1 ⅛yards
without cornerstones
Join blocks into rows with the short sashes first, then join the rows with the long strips.Press toward the sashing and the crossings nest.
- Quilt grows to58 × 70 in
- Short sashes24 · cut 2.5″ × 10.5″
- Long rows5 · 58″ each (pieced from strips)
- Sashing fabric1 ⅛ yd
The Formulas
Without Cornerstones
short sashes = (across − 1) × down, each one block long · long rows = down − 1, each the quilt’s widthWith Cornerstones
every sash is one block long · cornerstones = (across − 1) × (down − 1), cut at sashing width + ½Cornerstones break the long rows into block-length pieces with a square at every crossing: more pieces, easier matching, and the crossings land true because the cornerstone seams lock them.
Worked Example
Thirty 10 in blocks, 5 × 6, with 2 in sashing, no outer ring, no cornerstones:
- Short sashes: 4 × 6 = 24 pieces, cut 2½ × 10½ in. Long rows: 5, each 58 in, the quilt’s width with sashing counted.
- Quilt grows to 58 × 70 in (from 50 × 60 blocks-only).
- Fabric: all pieces as 2½ in strips → about 1⅛ yd.
How to Choose Your Inputs
- Sashing width: a quarter to a third of the block reads balanced: 2–3 in against a 10 in block. Wider sashing floats the blocks apart.
- Cornerstones cut at sashing width + ½ in square, in a contrast fabric.
- Outer sashing doubles as a first border; the border calculator takes over for anything wider.
Assumptions and Defaults
- All strips cut at finished width + ½ in from 40 usable inches, joined where a row outruns the fabric.
- With cornerstones, long rows become block-length sashes and the cornerstone squares price separately on their own row.
- Yardage rounds up to the next ⅛ yard.
Sashing Questions, Answered
How wide should quilt sashing be?
Quilt sashing is usually a quarter to a third of the block size, so 2 to 3 in suits a 10 in block. Narrower sashing reads like grout lines, whereas wider sashing sets the blocks apart like framed pictures, and all of these are established styles.
How much does sashing grow my quilt?
Sashing grows a quilt by its width once for every strip between blocks: 5 × 6 blocks of 10 in with 2 in sashing grow from 50 × 60 in to 58 × 70 in. Outer sashing around the edge adds twice its width more, bringing the same quilt to 62 × 74 in, and the calculator updates the size with every change.
Why use cornerstones in quilt sashing?
Cornerstones make the sashing crossings line up on their own, because every intersection becomes one seam meeting another instead of a long strip passing by. They also break long sashing rows into short pieces, which are easier to cut, and in a contrasting fabric they add a design element of their own.
Do I add sashing row by row or block by block?
Sashing goes on block by block first, with short sashes joining the blocks into rows, and then long strips, or rows of sashing and cornerstones, join the rows together. Press toward the sashing throughout, and the seams at each crossing will nest neatly.