You can calculate it, just remember that a normal win (thumbs down) in bronze is 4, silver is 6, gold is 9 and platinum is 12. Thumbs up gives double.
So [(electrum gained)/(base reward)] - (# of wins) = the thumbs up that you got, provided that you started with zero electrum when your deck didn't have any wins yet, and that you didn't reach top 10.