Coins in 5e are 50 to the lbs.If my numbers are right the coin portion of a tier one hoard from the DMG has an average weight of around 322 pounds @ 1/10 lb each. Personal encumbrance issues aside, I think it potentially great fun to give a 1st level party say, 10 000 silver trove and let them explain their plan to move 1 000 pounds of weight --
So 10,000 coins are 200 lbs. Still a lot.
(A medium modern coin, like a quarter, is 80 to the lbs. A 1 euro coin is 60 to the lbs. Note that gold is denser; so a gp is a big smaller than a US quarter in volume, but larger than a dime)
