Whether it's MDF, plywood, particle or melamine board, they all are over-sized because they're out of square. Melamine board, in particular, even has wavy edges.
Set your fence to take 1/8" off one long side and cut. Turn the sheet 180 degrees so the trailing becomes the leading short edge and cut 1/8" off the other long side. Now each long edge is parallel to the other and all panels indexed off these edges will be square.Wish you had a table saw? Drill holes in the four corners of your circular saw platen and screw it to a piece of plywood with the blade all the way up. Put the plywood on some saw horses, turn on the saw and let the blade down until it cuts through. Turn the saw/plywood over and Bingo! Use a long piece of heavy L-channel and 2 clamps for a fence.
Best good enough cheap table saw: Skil 8". Put a Freund TK series thin kerf blade on for $25. All you need to cut plywood or MDF if you're careful with fence adjustment. Towards X-mas they'll be around for under $200. Think you need something better? A guy I know turns out 2-3 kitchens a week with one he bought used! Now when asked why he doesn't buy something better, he says, "why"?
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