Quilting guide

How to add sashing and cornerstones to a quilt

Updated October 5, 2026 by Khokhar Sab

Cut each sashing strip 2½ inches wide for 2 inch finished sashing, and as long as the unfinished block. Cut cornerstones as squares the same width as the strips. Sew rows of blocks and short strips, sew rows of strips and cornerstones, then join the rows so the cornerstones line up with the strips between the blocks. Twenty 12 inch blocks set 4 by 5 with 2 inch sashing make a 54 by 68 inch center.

What sashing and cornerstones are

Sashing is the set of fabric strips sewn between quilt blocks. It frames each block and gives the eye a place to rest. Some patterns call it lattice.

Cornerstones are small squares that sit where a vertical strip meets a horizontal strip. They add a spot of contrast at every crossing. They also make the quilt easier to sew, because you join short pieces instead of long strips.

How to pick a sashing width

There is no fixed rule. Narrow sashing keeps the blocks close together. Wide sashing spreads them out and makes the quilt bigger with fewer blocks.

The Missouri Star Quilt Company suggests 2 to 3 inches finished for 12 inch blocks and 2 to 2½ inches for 10 inch blocks. For 6 inch blocks it suggests 1 to 1½ inches. As blocks get smaller, the sashing shrinks with them so it doesn't swamp the design.

The table shows what different widths do to the same 20 blocks: 12 inch finished blocks, 4 across and 5 down, with cornerstones and no borders.

The fabric columns assume 42 inch fabric with 2 inches of selvage trim and 10 percent extra, rounded up to ⅛ yard. Doubling the sashing from 1½ to 3 inches adds only ½ yard, because the strips are short and many fit across the fabric. Cornerstones barely register: even at 3 inches the 12 squares need ¼ yard, so scraps can cover them.

Choosing sashing and cornerstone fabric

Sew Nikki's sashing tutorial suggests picking a sashing color that brings in a hue your blocks are missing. Cornerstones are small, so they suit a contrast fabric or scraps. Artquiltmaker cut hers from scraps, at only 1½ inches square.

Cut sizes: finished width plus ½ inch

Every piece in a quilt loses ¼ inch to the seam on each side. So you cut each piece ½ inch bigger than the size you want to see.

• Sashing strips: cut them 2 + ½ = 2½ inches wide for 2 inch finished sashing.
• Strip length: cut them the same length as the unfinished block. A 12 inch finished block measures 12½ inches before you sew it in, so each strip is 2½" × 12½".
• Cornerstones: cut squares the same size as the strip width, 2½" × 2½".

For the 4 by 5 layout, that is 31 strips and 12 cornerstones. Each of the 5 block rows has 3 strips, and each of the 4 sashing rows has 4 strips.

How sashing changes the quilt size

Without sashing, the quilt center is just the blocks: 4 × 12 = 48 inches wide and 5 × 12 = 60 inches long.

Sashing between the blocks adds one strip fewer than the number of blocks. Four blocks across have three gaps, so the width grows by 3 × 2 = 6 inches to 54 inches. Five blocks down have four gaps, so the length grows by 8 inches to 68. The general rule:

width = blocks × block size + (blocks − 1) × sashing

Some quilts also have sashing around the outside of the grid. That adds two more strips to each direction, so the same layout becomes 58 by 72 inches and needs 30 cornerstones instead of 12.

Sew Nikki's log cabin quilt is a real example of outer sashing. It has 42 blocks of 12 inches finished, set 7 across and 6 down, with 2½ inch cut sashing all around. Her cutting list calls for 97 sashing strips and 56 cornerstones. The calculator, with outer sashing switched on, gives 97 strips and 56 cornerstones, and a 100 by 86 inch center before borders.

Borders come after that. With the calculator's default 2 inch inner border and 4 inch outer border, the finished quilt is 66 by 80 inches. Compare that with the quilt size chart to see which bed it fits.

Planning blocks for a size you want

Sashing also changes how many blocks you need. Say you want a quilt center about 60 inches wide from 12 inch blocks. With no sashing, 60 ÷ 12 = 5 blocks fit exactly.

Add 2 inch sashing and each block takes up 14 inches, counting the strip beside it. Now 4 blocks is the closest fit, for a 54 inch center. You make fewer blocks, and you can add a border to reach the full width. The quilt layout calculator does this for both directions in its "I want a size" mode.

Sashing without cornerstones

You can skip cornerstones and use one long strip between each pair of rows. For the same layout, you cut each long strip 54½" long. That is longer than the 40 usable inches across 42 inch fabric once you trim the selvages, so you have to join strips to get that length.

Long strips are harder to line up, because nothing marks where the blocks above and below should sit. Mark the edge of each block on the long strip with a pin or a chalk dot before you sew it on.

How to add sashing and cornerstones to a quilt, row by row

1. Square up every block to the same size. Sashing makes small size differences easy to see.
2. Sew block rows: block, strip, block, strip, ending with a block (or with a strip if you have outer sashing).
3. Sew sashing rows: strip, cornerstone, strip, cornerstone, ending with a strip.
4. Press every seam toward the sashing, in both kinds of row.
5. Pin a sashing row to a block row so each cornerstone sits right over a vertical strip. The seams will nest against each other because you pressed them in opposite directions.
6. Sew the rows together, then press those long seams toward the sashing rows.

Check that each sashing row is the same length as the block rows before you join them. If one is short, look for a seam that drifted from ¼ inch. Fixing it now is far easier than easing in a long row later.

Sew Nikki adds two layout tips. Lay the blocks out on a bed or the floor to balance the colors. Then put a pin in the top-left block of each row so the rows don't get mixed up on the way to the machine. She also skips pressing between row joins to keep the fabric pliable while matching seams. That differs from the press-every-seam approach above, so try both on a test row.

Sewing in sections instead of rows

Artquiltmaker's sashing class calls rows the common way, then sews the quilt in chunks instead to avoid long row seams. The method works with cornerstones:

1. Sew a vertical sashing strip to the right side of each block.
2. Sew a horizontal strip to a cornerstone, and press.
3. Nest the seams and sew that strip-and-cornerstone piece to the top of the block.
4. Sew the units together in small groups, pinning at each seam, until only one long seam remains.

Each unit is a block with sashing on two sides, so the seams you join are short. The author finds it more precise than rows. Blocks along the top or right edge get only the sashing they need, depending on whether the quilt has outer sashing or goes straight to a border.

For the yardage of the strips, cornerstones and borders, enter your layout in the quilt layout calculator. The Missouri Star blog has a longer sashing guide with more width examples. If you set blocks diagonally instead, see how to set quilt blocks on point.

Sources and further reading

• Missouri Star: sashing in quilting, with math.
• Artquiltmaker: setting the blocks together.

Video tutorial

"Let's Make! | Cornerstones and Sashing Tutorial" by Jordan Fabrics, on YouTube. The video loads only when you press play.