How to use the quilt sashing and border calculator
- Enter the blocks across and blocks down, and the finished block size in inches.
- Enter the sashing width between blocks and the border width. The 2 and 4 shown are examples. Use 0 to leave either out.
- Open More options if your seam allowance is not 1/4 inch.
- Read the finished quilt size and the table of pieces with their cut sizes.
Formula
width inside the border = blocks across x block + (blocks across - 1) x sashing
quilt width = width inside the border + 2 x border
sashing strips = (across - 1) x down + across x (down - 1)
cornerstones = (across - 1) x (down - 1)
The same formulas apply to the length with the blocks down. Cut sizes add two seam allowances to each finished measurement.
Three by three blocks of 12 inches
Three blocks across at 12 inches plus two 2 inch sashing strips make 3 x 12 + 2 x 2 = 40 inches. Add a 4 inch border on both sides and the quilt is 48 inches wide. The length works out the same, so the quilt is 48 x 48 inches. It has 9 blocks, 12 sashing strips and 4 cornerstones.
With 1/4 inch seams, blocks cut at 12 1/2 inches, sashing strips cut 2 1/2 x 12 1/2, and cornerstones cut 2 1/2 inches square. The side borders are cut 4 1/2 x 40 1/2 and the top and bottom borders 4 1/2 x 48 1/2.
How the layout goes together
Sashing is the strip between blocks. In each row, strips go between neighboring blocks. Between rows, a long strip is made of sashing strips and cornerstone squares in a line. Counting the pieces first makes it easier to cut them in batches.
Borders are measured after the center is sewn. Real piecing can differ a little from the plan, so measure the finished top through the middle and cut the borders to that number rather than trusting the arithmetic alone.
Next steps
Once you know the quilt size, estimate the back and edge with the Quilt Backing and Binding Calculator. To convert block sizes, use the Quilt Block Size Calculator, and for triangle units in the blocks, the Half Square Triangle Calculator.
Assumptions and limits
- Blocks are the same size and the sashing and border widths are the same all around.
- Cut sizes add the seam allowance on both sides of each piece.
- Side borders are sewn first and the top and bottom borders are sewn across them.
- Fabric yardage is not calculated here. Use the cut list to plan it.
Frequently asked questions
How do I calculate the size of a quilt with sashing and borders?
Add the blocks and the sashing strips between them for each direction, then add the border width on each side. Three 12 inch blocks with 2 inch sashing and 4 inch borders make a 48 inch quilt.
How many sashing strips and cornerstones do I need?
For a grid of blocks, the strips are (across - 1) x down plus across x (down - 1), and the cornerstones are (across - 1) x (down - 1). A 3 by 3 layout needs 12 strips and 4 cornerstones.
What size do I cut the border strips?
Cut the border width plus two seam allowances by the length of the center edge it is attached to, plus two seam allowances. Measure your finished top before cutting to confirm.
Do I need cornerstones?
Not always. Cornerstones are small squares where sashing strips cross. Some quilts use sashing that runs in solid lines instead. Set the sashing width to 0 to see a quilt with no sashing at all.