What is the legal (Shariah) nisab for paying zakat on money, and is it measured by gold or by silver?

Paper currency is subject to the condition of reaching the nisab, which is equivalent to the value of 85 grams of gold or 595 grams of silver. Sheikh Yusuf Al-Qaradawi preferred that the estimation by gold is more appropriate, as it is a safer approach and a stronger argument, even though estimation by silver is more beneficial for the poor. However, he considered that to be unfair to those with wealth. This is what we lean towards and issue fatwas accordingly.