Does anyone know what coins weigh? How do you handle this in your game? the question came up and I hadn't really thought about it since the D&D days and cant remember what we used then even.
the most realistic way is 64 coins to a pound...DND used to use a much smaller amount to make a pound but having each coin weight 1/4 ounce is a decent method.
If you dont like that round it off and use 50 to a pound or something like that.
In addition to this, my campaign uses "Trade Bars" which are one pound (50 coins) in weight. It makes large purchases a little more beliveable from a roleplaying perspective.