A basic floor cushion pattern that may be adapted to fit various sizes of cushion inserts.

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Two pdf versions are available: one with several helpful pictures, and a “print version” with fewer pictures.

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From the pattern website:
I love to invite friends over to watch a movie or play some board games, but it felt inhospitable to ask them to endure sitting on my anything-but-plush “carpet.” And in my cramped university apartment, space is a commodity that must be used efficiently! So I designed this as a simple project that could be conveniently stacked in a closet or stored beneath a futon.

I’m all about instant gratification, and this project turned out to be fairly quick and satisfying—after all, it’s mostly just panels of stockinette stitch seamed together.

Note: You can adjust the pattern to fit whatever size cushion insert you would like; 16”x16”x4” is just what I was able to find in the craft section at my local mass-merchandising store (hence the 16”x16” top/bottom panels and the 16”x4” side panels).