The size issue is one of value, based on the metals. In the US, the penny has always been copper, since the early eighteen hundreds, and has always been (roughly) the same size. There were two cent coins, which were about twice as big, and the original five cent coins were huge copper monstrosities. The relative value of nickel to copper allowed them to make a five cent piece (nickel) much smaller. The dime, a $.10 piece, was made of silver originally, and so is considerably smaller than a penny. The quarter ($.25), $.50 piece, and silver dollar were all proportional to weight, with the silver dollar being a full 1 ounce of silver (until '63, when silver-clad copper started being used...) They were very large, and anything of larger denomination was made of gold. There was a gold one dollar coin minted for a while, but it was smaller than a dime.
The current "golden dollars" that the US has been minting for quite awhile now (no gold involved) are closer to the old gold ten dollar pieces in size, which makes roughly the same size as a quarter, which is a constant complaint about the coins.
Sorry, I come from a long line of US coin collectors, and though the only thing I collect are wheat back pennies (my prize is a 1909 VDB I found in change), different parts of the family have everything from prerevolutionary coins through every mint set ever put out!
In other words, we've hit one of my nerd spots...
And it's Sunday afternoon. What else am I gonna do while waiting?