Quilt layout, sashing and borders.

Answer

A quilt of 4 x 5 blocks of 12 in with 2 in sashing, a 2 in inner border and a 4 in outer border finishes at 66 x 80 in. With sashing, the width is blocks x block size + (blocks - 1) x sashing, plus both sides of every border.

Worked example

Across: 4 x 12 + 3 x 2 = 54 in. Down: 5 x 12 + 4 x 2 = 68 in. Borders add 2 x (2 + 4) = 12 in each way, so the quilt is 66 x 80 in. Pieces: 20 blocks, 15 short sashes between blocks in a row (2 x 12 in finished), 16 sashes between the rows (12 x 2 in) and 12 2 in cornerstones. With a 1/4 in seam, blocks are cut 12.5 in and sash strips 2.5 in wide. Inner border: two sides 68 in long, then top and bottom 58 in. Outer border: sides 72 in, top and bottom 66 in. For a target of 70 x 90 in the largest grid that fits is 4 x 5 blocks, finishing 66 x 80 in.

How it works

All sizes are finished sizes (after sewing). Cut sizes add two seam allowances. Borders are added sides first, then top and bottom, so the top and bottom strips span the width of the quilt plus the two side borders just added. Strip lengths shown are finished lengths; add a few inches to cut long and trim to measured length. Sashing pieces: short sashes between blocks = rows x (columns - 1); sashes between rows = (rows - 1) x columns; cornerstones, the small squares where sashing crosses, = (rows - 1) x (columns - 1). This is plain arithmetic on the numbers you enter.

FAQ

How do I work out the finished size of a quilt with sashing?

Add the blocks and the sashing between them: width = blocks across x block size + (blocks across - 1) x sashing width. Do the same for the length, then add both sides of each border.

How many sashing strips and cornerstones do I need?

For 4 x 5 blocks you need 15 short sashes between blocks in rows, 16 sashes between rows and 12 cornerstones. The calculator works the counts out for any grid.

What size do I cut sashing and border strips?

The finished width plus two seam allowances, so 2.5 in for 2 in sashing with a 1/4 in seam. Cut border strips a little long and trim to the measured length.

How many blocks fit a given quilt size?

Enter a target width and length. The tool finds the largest grid of blocks that fits inside the borders, which gives the nearest size not over your target.

Can I use it without sashing or borders?

Yes. Set the sashing and borders to 0 and the result is just blocks across times blocks down times block size.