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   Two plates with a separate boxing. This is the most common cushion type. It can easily be fashioned with piping all round either the top or the bottom edges. The boxing runs smoothly and continuously round corners: that is, there will be no vertical seams at the corners. A zipper opening along the back edge is used to insert foam.

  This calculator is limited to square or rectangular shapes. Even so it can be useful with any four sided shape if plates are marked for maximum height and width and then adjusted to final shape before cutting.

  This four sided cushion type features a top plate that includes fabric on the sides to create boxing that is folded over the edges. The sewn corner edges are termed "boxed corners".

  The bottom plate is often fabric with a zipper opening but it can be a simple "backing board" or "platform".

  A square or rectangular box corner cushion completely wrapped in a single piece of fabric. A seam will run down each "boxed" corner.

  A zipper is on one long edge to provide for foam insertion and removal.

  A square or rectangular top plate (irregular shapes are possible with adjustments prior to cutting) with a separate continuous boxing (no corner seams) intended to be secured to a backing board or platform (usually with staples).

  Intended for those who are building cushions for sailboat V-births with four sides -- one of those sides bounded by two right angles, but plates can be modified prior to cutting for more complicated shapes.