If the size is a matter of concern, they are the same amount larger than a quarter as a quarter is than a nickel.

The quarter is very slightly larger in diameter than a nickel, but slightly thinner. They both contain nearly the same volume of metal.

The quarter and the nickel are so close to the same size that you can squeeze a nickel between two good flat steel plates and make it the same diameter and nearly identical weight and thickness as a quarter. Close enough to work in nearly any vending machine that takes quarters. (actual test result)

Of course it does take about 17,000 pounds of squash to do it (same test). Nickels are pretty $@#%! hard.

You can't really tell a nickel from a quarter by feel except for the knurl on the quarter and smooth edge on the nickel. The diameters are just different enough that if you have one of each, with them side to side, you can feel which is which by the difference, but if you just take one at a time out of your poke you'll have a hard time telling which you've got other than by the knurl.

John