D&D uses five coins, and the standard unit is the gold piece (gp). Everything converts in clean multiples: 1 gp = 10 silver (sp) = 100 copper (cp). Platinum sits above gold, and electrum is an odd in-between coin many tables ignore.
The full ladder: 1 platinum (pp) = 10 gp, 1 gp = 2 electrum (ep) = 10 sp = 100 cp, and 1 sp = 10 cp. So a single platinum piece is worth 1,000 copper, and 50 copper is half a gold.
Rulebook prices are listed in gold, silver, and copper, so converting a hoard into one unit makes it easy to split loot evenly. Coins weigh about a fiftieth of a pound each — 50 coins to the pound — which starts to matter once you’re hauling thousands of them.