Cushion fabric calculator: how the answer is worked out
Panel size = cushion size + 2 in (1 in seam allowance on each side). Fabric per cover = 2 panels. Length to buy = how many rows of panels fit across a 44 in roll x panel height. For the four preset sizes: a 12 in cushion takes two 14 in panels (392 sq in), three fit across the roll, so 14 in (0.36 m) of fabric; 16 in takes two 18 in panels (648 sq in) in 18 in (0.46 m); 18 in takes two 20 in panels (800 sq in) in 20 in (0.51 m); 24 in takes two 26 in panels (1,352 sq in), only one fits across, so 52 in (1.32 m). For four 16 in covers the eight panels sit two across in four rows: 72 in (1.83 m). The 1 in allowance and 44 in roll are StitchMagic calculator defaults; if your fabric pattern needs matching across panels, buy extra.
Cushion cover sizes
The calculator’s presets are 12, 16, 18 and 24 in square, and the size box takes any other size. Measure the cushion insert edge to edge across the middle and enter that number; the calculator adds the seam allowance itself, so do not add it twice. The size printed on an insert’s label is the size to enter.
Fabric calculator for rectangular and round cushions
The calculator works in squares. For a rectangular pillow or cushion, add 2 in to each side and double it: a 12 x 20 in cushion takes two 14 x 22 in panels, 616 sq in. For a round cushion, enter the diameter: each round panel is cut from a square of diameter + 2 in, so the fabric is the same as for a square cushion of that size; the offcuts from the corners can go into piping.
Box cushion calculator
A box cushion has a top, a bottom and a side strip (gusset) that runs all the way round. Top and bottom: cushion length + 2 in by width + 2 in each. Gusset: the cushion’s perimeter + 2 in long, and its depth + 2 in wide. Example, an 18 x 18 x 3 in seat cushion: two 20 x 20 in panels (800 sq in) and a 74 x 5 in gusset (370 sq in), 1,170 sq in in all. A gusset longer than your roll is wide can be cut in two strips and joined; add 2 in for the joining seam.