Actually, Assuming that I am correct that 1cm = 10mm that would be = to about 2 1/8th x 3 3/8th according to my ruler. It is measured out in CM but has 10 marks between each CM. I assume those marks are each a MM. Incidentally, I did measure one of my regular chips and it did, in fact, measure out to just less than 4cm. That would be consistant with 39mm.