The value of the niṣāb is calculated in dinār coins and dirḥam coins. The dinār is a gold coin weighing one mithqal (4.25 grams) and the dirḥam is a silver coin weighing 0.7 mithqal (2.975 grams). The relation between 20 dinārs and 200 dirḥams which is part of the definition of niṣāb reflects the contemporary exchange value between the dinār and the dirḥam of 1 to 10 in the early days of Islam. In later times the exchange rate between the two Sharia coins changed according to market values, and so exchange rates of 1 to 11 and 1 to 12 are seen in early fiqh literature. This exchange rate has varied even more in the last few centuries. The shift in exchange rate meant that in later times 20 dinārs became more expensive in market value than 200 dirḥams. Despite this the definition of niṣāb has not been altered throughout Islamic history, and therefore a choice is created between the value of 20 dinārs and the value of 200 dirḥams. Both values are accepted in Shariah, and so one can choose to pay the value of either of them.