A quilt that ends up the wrong size is nearly always a planning problem, not a sewing problem. The steps are short: choose the finished size, decide how big each block will be, work out how many fit, and add sashing or borders until the total comes out close to the target.
Start with the finished size
The quilt size database lists the standard dimensions in inches. A few points from it:
| Quilt | Mattress | Typical quilt |
|---|---|---|
| Baby | none | 30 to 36 x 40 to 52 |
| Crib | 28 x 52 | 36 to 45 x 52 to 60 |
| Lap or throw | none | 50 to 60 x 60 to 72 |
| Twin | 38 x 75 | 64 to 72 x 86 to 96 |
| Full | 54 x 75 | 78 to 86 x 86 to 96 |
| Queen | 60 x 80 | 84 to 96 x 92 to 108 |
| King | 76 x 80 | 100 to 112 x 92 to 108 |
A bed quilt is bigger than the mattress because it has a drop over the sides. A drop of 8 to 12 inches reaches the top of the legs; 15 to 20 inches reaches the floor. To find a width, add twice the drop to the mattress width, and to find a length add the drop at the foot, plus about 10 to 12 inches if the quilt will tuck under the pillows. Check the mattress depth too, since thick mattresses need a longer drop for the same appearance.
Choose the block size
Blocks are chosen in whole inches, such as 6, 8, 10, 12 and 16 inches finished, since these are easy to cut from standard rulers and easy to divide. A block that is 12 inches finished is 12.5 inches when cut, to allow for the seam allowance. The blocks database shows the grid each traditional block is drawn on: a Nine Patch is a 3 by 3 grid, a Sawtooth Star is based on a 4 by 4 or 5 by 5 grid. Choose a block size that divides evenly by the grid. A 12 inch Nine Patch has 4 inch units; a 9 inch one has 3 inch units, which are simpler to cut.
Count the blocks
Divide the target width by the block size and the target length by the block size, and round to a whole number. For a lap quilt of about 50 x 62 inches with 10 inch blocks, that is 5 across and 6 down, which is 30 blocks and a top of exactly 50 x 60 inches.
If the numbers do not divide evenly, add a border. A top with 4 by 5 blocks of 12 inches is 48 x 60; adding a 6 inch border on each side gives 60 x 72, the top of the lap size.
Add sashing
Sashing is strips between blocks. It gives each block room, lets you use fewer blocks and makes a setting easier to fit to a size. For a grid of m blocks across and n blocks down with sashing of width s:
- Width = m x block + (m − 1) x s
- Length = n x block + (n − 1) x s
For a 3 by 4 grid of 12 inch blocks with 2 inch sashing, width is 36 + 4 = 40 inches and length is 48 + 6 = 54 inches. A 4 inch border all round adds 8 to each: 48 x 62. Cornerstones, small squares where sashing strips cross, are the same width as the sashing.
Borders
Plan borders last, to absorb a size that is slightly off. A border of 3 to 6 inches frames the quilt, and several borders in turn can add width quickly. For a bed quilt, a wide final border, 8 to 12 inches, is a cheap way to add drop.
Borders should be cut to the measurement through the middle of the quilt, not the edge, which the next article on wavy edges covers. A border width also affects binding and backing: add 4 inches to each side of the top for the backing, and plan fabric for the quilting process.
On-point settings
Blocks set on the diagonal look different but need more planning. The diagonal of a block is its side times 1.414, so a 10 inch block has a 14.14 inch diagonal. Extra setting triangles fill the edges. Patterns usually give the sizes; if you design your own, use a drawing or a grid paper to count.
Fabric per size
The larger the top, the more backing and batting are needed. A quilt top larger than about 40 inches in either direction needs a pieced backing unless you use a wide fabric. The yardage calculator gives the amounts of each colour, backing, batting and binding for a quilt of squares, from the finished size, so after you have settled the layout, enter it and buy the total.
A worked example
Target: a twin-size quilt, about 66 x 88 inches.
- Block: 11 inch finished.
- Blocks across: 5 gives 55 inches; blocks down: 7 gives 77 inches.
- Borders: 5.5 inches each side gives 66 x 88.
- Total: 35 blocks plus borders.
- Backing: 66 + 8 = 74 by 88 + 8 = 96 inches.
The checklist: size, block, count, sashing, border, then fabric.