What thickness should a mousepad be for an uneven desk?

Get a mousepad that is at least 5mm thick. For a noticeably uneven desk, go 7mm to 10mm — the thick foam fills in dips and bumps better than thin pads. But avoid going over 10mm, as that can tilt your wrist up and cause strain. The sweet spot is 5-7mm: enough to smooth things out without bending your wrist.