How Much Sashing Fabric Do You Need?
Use this quilt sashing calculator to turn a block layout into a practical cutting and fabric plan. Enter the finished block size, blocks across and down, finished sashing width, usable width of fabric and whether you want cornerstones. The calculator returns the sashing piece count, cut sizes, WOF strips, fabric yardage, cornerstones and finished quilt dimensions.
If you add cornerstones, the calculator breaks the horizontal sashing into block-length pieces and counts the squares at each intersection. Without cornerstones, it calculates full horizontal sashing rows and includes the fabric needed to piece any strip that is longer than one usable fabric width.
Quick Quilt Sashing Chart
This quick table uses 10-inch finished blocks, 2-inch finished sashing, 1/4-inch seams, 42-inch usable fabric, cornerstones from the same fabric, 5% extra and purchase rounding to the next quarter yard. It does not include a separate outer sashing border.
| Block layout | Finished quilt size | Internal sashing pieces | Cornerstones | Recommended fabric |
|---|---|---|---|---|
| 4 × 5 | 46 × 58 in | 31 | 12 | 0.75 yd |
| 5 × 6 | 58 × 70 in | 49 | 20 | 1.25 yd |
| 6 × 7 | 70 × 82 in | 71 | 30 | 1.5 yd |
| 7 × 8 | 82 × 94 in | 97 | 42 | 2.25 yd |
Use your own measurements before buying fabric. Rectangular blocks, a different sashing width, separate cornerstone fabric, an outer sashing border or a narrower usable WOF will change the result.
How to Calculate Sashing Between Quilt Blocks
Sashing is the fabric that separates quilt blocks. The number of pieces depends on the number of block gaps rather than the number of blocks alone.
Vertical sashing pieces = rows × (columns − 1)
When cornerstones are used:
Horizontal sashing pieces = columns × (rows − 1)
Internal cornerstones = (columns − 1) × (rows − 1)
Without cornerstones, the calculator replaces those short horizontal pieces with one continuous sashing row between each block row. If that row is wider than your usable fabric width, the cutting plan allows for the join needed to build the longer strip.
Finished Sashing Width vs. Cut Width
Enter the width you want the sashing to show after sewing. The calculator adds seam allowance on both sides to give you the cut width.
Sashing cut width = finished sashing width + (2 × seam allowance)
For example, 2-inch finished sashing with 1/4-inch seams is cut 2.5 inches wide. A short sashing piece placed beside a 10-inch finished block is cut 10.5 inches long because the block and sashing piece both need seam allowance at the ends before the rows are joined.
How Sashing Changes the Finished Quilt Size
Sashing adds space only in the gaps between blocks. Five 10-inch blocks across have four internal gaps. With 2-inch finished sashing, the center finishes 58 inches wide.
Finished quilt width = (blocks across × finished block width) + ((blocks across − 1) × finished sashing width)
Finished quilt height = (blocks down × finished block height) + ((blocks down − 1) × finished sashing width)
If you select an outer sashing border, its finished width is then added to both sides of each dimension.
Sashing With Cornerstones
Cornerstones are small squares placed where horizontal and vertical sashing meet. In a regular layout, their finished size matches the finished sashing width, so their cut size matches the sashing cut width.
The calculator can treat the cornerstones as part of the sashing fabric purchase or as a separate fabric. When you choose separate fabric, it reports the recommended cornerstone purchase independently.
Sashing Without Cornerstones
Without cornerstones, the usual row construction uses short vertical sashing pieces inside each block row and long horizontal sashing strips between completed rows. Those horizontal strips span the width of the block-and-sashing row.
For larger quilts, one horizontal strip can be longer than the usable WOF. The calculator checks that length and includes straight or diagonal strip joins according to the option you select.
Worked Example: 5 × 6 Blocks With 2-Inch Sashing
Suppose you have five 10-inch finished blocks across and six down. You want 2-inch finished sashing, 1/4-inch seam allowance, 42-inch usable fabric and cornerstones cut from the same fabric.
The vertical count is 24 pieces, the horizontal count is 25 pieces, and the layout needs 20 cornerstones. Each short sashing piece is cut 2.5 inches wide and 10.5 inches long. The finished quilt center becomes 58 × 70 inches. With the assumptions used in the quick chart, the recommended purchase is 1.25 yards.
Use the Usable Fabric Width
Use the width left after removing selvages rather than relying on the bolt label. A smaller usable width can increase the number of WOF strips or force an additional join in a long horizontal sashing row.
Outer Sashing Around the Quilt
Turn on Outer sashing border when you want the same narrow framing treatment around the outside of the block grid. You can give it a different finished width and choose whether to use four cornerstones at the outside corners.
If you are adding a wider decorative border, calculate that separately with the Quilt Border Calculator.
Quilt Sashing Calculator FAQ
How do I calculate how much sashing I need for a quilt?
Use the finished block size, blocks across and down, finished sashing width and usable width of fabric. Count the gaps between blocks, add seam allowance to the cut dimensions, then determine how many WOF strips are required. This calculator performs those steps and converts the cutting plan into yardage.
How many sashing strips do I need for a 5 × 6 block quilt?
With cornerstones, a 5 × 6 layout needs 24 vertical sashing pieces and 25 horizontal pieces, for 49 short sashing pieces total, plus 20 internal cornerstones. Without cornerstones, it still needs 24 vertical pieces but uses five long horizontal sashing rows instead.
What size should I cut 2-inch finished sashing?
With a 1/4-inch seam allowance on each side, cut the sashing 2.5 inches wide. The length depends on whether it is a short piece beside a block or a continuous row across the quilt.
How many cornerstones do I need?
For internal cornerstones, multiply one less than the columns by one less than the rows. A 5 × 6 block layout needs 20 internal cornerstones.
Are cornerstones the same cut size as the sashing width?
Their finished size normally matches the finished sashing width. Their cut size includes seam allowance on all sides, matching the sashing cut width.
Can I calculate sashing without cornerstones?
Yes. Choose the no-cornerstone option. The calculator uses long horizontal sashing rows between completed block rows and checks whether those rows need to be pieced.
Can the cornerstones use a different fabric?
Yes. Choose separate cornerstone fabric and enter its usable width. The result shows a separate recommended purchase for that fabric.
Does sashing make a quilt bigger?
Yes. Every internal gap adds the finished sashing width. The calculator reports the resulting finished quilt size before any separate decorative border is added.
Related Calculators
Continue planning your quilt with the Quilt Block Calculator, Quilt Border Calculator, and Quilt Binding Calculator.