1- The nisab for dollars or other currencies is whatever is equivalent to the value of 20 mithqals of gold or 140 mithqals of silver at the time when the zakah is owed. 2- The nisab for silver is roughly equivalent to 595 grams of silver, so the one who has wealth has to pay 2.5% or 25 out of every 1,000 that he has in currency, after one year has passed.