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Box Cushion Fabric Calculator
A box cushion (also called a bench, banquette or seat cushion with sides) is cut as a top panel, a bottom panel, and a boxing strip that wraps the front and two sides. The back boxing is usually split into two overlapping strips so a zipper can be inserted. Because the boxing strip is one continuous piece, its length is driven by the cushion's perimeter, not just its width — that's the number most people get wrong when they estimate by eye.
Cutting list
| Piece | Qty | Size |
|---|
Cutting layout
Typical sizes
Indoor bench cushions commonly run 18–24 in (46–61 cm) deep and however long the bench is; outdoor and window-seat cushions are frequently 4–5 in (10–13 cm) thick. A 3-seat sofa bench cushion set is usually three separate box cushions rather than one long one, because a single long cushion sags in the middle.
Where this goes wrong
Fabric with a directional pattern can't be rotated 90° to save yardage on the boxing strip, so railroaded (sideways-printed) fabric is worth asking your supplier about for long benches. Foam is normally cut about 1/2 in (1.3 cm) larger than the finished cover on each side for a tight, wrinkle-free fit — size the cover to the foam, not the seat opening.
Seam allowance
Upholstery seam allowance is conventionally 1/2 in (1.3 cm). Piping/welt adds its own allowance — see the piped cushion calculator if your boxing has corded seams.