This varies from country to country, along with the sizes and weights of the various coins, the reason that bankers and others - such as Bran al'Vere - use scales for comparing coins. The heaviest coins in weight of precious metal come from Andor and Tar Valon. For the coins of those two, the scale is very simple.

Ten copper pennies = one silver penny.
One hundred silver pennies = one silver mark.
Ten silver marks = one silver crown.
Ten silver crowns = one gold mark.
Ten gold marks = one gold crown.

As an example of other countries' currencies, the scale for Altara, where the weight of silver or gold in larger coins is less than that in Andor or Tar Valon, is this:

Ten copper pennies = one silver penny.
Twenty-one silver pennies = one silver mark.
Twenty silver marks = one silver crown.
Twenty silver crowns = one gold mark.
Twenty gold marks = one gold crown.