This is mine, it is mainly for you to easily see the numbers, you could change them any way you like.
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tp to dollar ratio = 100:1 (5,000 tp/$50 tp code, since this is what people use to trade)
tp to shard ratio = 5:1
tp to plat ratio = 1:1000
So here it goes, currencies from higher value to lower value:
$1 = 20 shards = 100 tp = 100,000 plat
Therefore plat per shard = 100,000/20 = 5,000 plat
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I usually don't think about these numbers while in game, because almost everything that cost shards is too costly, without a thought.
Example: First Level 1 hire on the list in Korthos costs 1 shard, so it's at least 1:1 ratio.
I can go on and on, but you get the idea.