What is the largest piece of plywodd I could fit in your car?

my buddy has a zx3. he is a math professor, and he wants chalkboards. they are $$$$ expensive. I want to make him a few with plywood and chalkboard paint. just wondering how big I can make them and still have 'em fit in his ride.

when i did my rear seat delete i bought a piece of 3x5 plywood and it fit comfortably with room to spare so i don't scratch anything up

excellent! thanks a million.