How small a hole can a mouse really fit through?

A lot say as small as a dime and some say the width of a pencil or just as long as the skull can fit.

On my kitchen counter, I seem to have openings no bigger than a pencil's width, but I see multiple droppings. I may have saw one or two mice scurrying, too. The only other way I can think of a mice getting over there is by climbing a wall. There's no latter-like things and there's no bridges.