How to add sashing to a quilt

30 September 2026 · Sashing guides

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What sashing and cornerstones are

Sashing is a frame of fabric strips between the blocks. It gives each block room, hides points that don't quite meet from block to block, and makes the quilt bigger without making more blocks. Cornerstones are the small squares where a vertical and a horizontal strip cross. With them, every sashing strip is the length of one block and the rows line up at the cornerstones. Without them, the horizontal sashing runs the full width of the quilt in one piece.

Sashing the same fabric as the block backgrounds makes the blocks float. A contrasting sashing draws a grid round them. Both are worth trying on screen before you cut: see how to audition fabrics before you cut.

How wide should sashing be?

There is no rule, only proportion. A rule of thumb several quilting guides repeat is a quarter to a third of the block's width: 3″ to 4″ for a 12″ block, 1½″ to 2″ for a 6″ block. Plenty of quilts go narrower. Narrow sashing reads as a line, wide sashing as a lattice. Sashing, the app, offers 1″, 1½″, 2″, 2½″ and 3″, and its starting layouts use 2″ between 12″ blocks.

Whatever the width, cut it ½″ wider: a ¼″ seam on each long edge. For 2″ finished sashing, cut 2½″.

How many strips and cornerstones to cut

For a quilt that is A blocks across and D blocks down, with cornerstones:

• Sashing strips: (A − 1) × D + (D − 1) × A, each cut to the sashing width + ½″ by the block size + ½″.
• Cornerstones: (A − 1) × (D − 1), each cut to the sashing width + ½″ square.

A throw of twenty 12″ blocks, four across and five down, with 2″ sashing, needs (3 × 5) + (4 × 4) = 31 strips of 2½″ × 12½″ and 3 × 4 = 12 cornerstones of 2½″.

Cut the strips the thrifty way. A 12½″-deep strip across 40″ of fabric gives sixteen 2½″ slices, so the 31 strips come from two 12½″ strips (25″ of fabric). Cutting eleven 2½″ strips and slicing three 12½″ lengths from each would use 27½″. The cornerstones come from one 2½″ strip. That is exactly what Sashing's cutting chart prints for this quilt: “(2) 12½″ × WOF, subcut (31) 2½″ × 12½″ rectangles”. If WOF is new to you, here is how to read a cutting chart.

Without cornerstones

You still cut (A − 1) × D short strips for between the blocks in each row. Between the rows you need D − 1 long strips, each the width of a joined row plus ½″. In the same throw, a row is 4 × 12″ + 3 × 2″ = 54″, so four strips of 54½″: 218″ in all, which is six 2½″ strips across the fabric joined end to end.

How to sew sashing on, step by step

1. Lay the blocks out in order, with the sashing strips between them.
2. Sew a short strip to the right side of every block in a row except the last, then sew the row together. Pin at both ends and the middle.
3. Press the seams toward the sashing. The sashing has no seams of its own, so it takes the bulk.
4. For cornerstones, sew the sashing rows: cornerstone, strip, cornerstone, strip, and so on, ending in a strip.
5. Sew a sashing row to the bottom of each block row, matching each cornerstone seam to a block seam, then join the rows.
6. Without cornerstones, measure a finished row before cutting the long strips to length, and mark where each block seam falls so the blocks line up from row to row.

Sashing changes the size of the quilt

Finished width = blocks across × block size + (blocks across − 1) × sashing width. Twenty 12″ blocks with no sashing are a 48 × 60″ quilt. With 2″ sashing they are 54 × 68″, and a 4″ border takes that to 62 × 76″. Plan the sashing before you decide how many blocks to make, or the quilt comes out larger than you meant. The quilt sizes chart has the common targets, and the border guide takes the maths one ring further out.