Praise be to Allah, and may Allah’s peace and blessings be upon the Messenger of Allah, his family and his companions. Wa alaikum assalam wa rahmatullahi wa barakatuh. As to what follows: In response to your question, we say: The nisab of gold is what was mentioned in the Prophet’s (peace be upon him) statement in authentic hadith that “There is no Zakat on less than five okes of silver” [al-Bukhari (1459) and Muslim (980). Five okes are equivalent to twenty mithqals. One mithqal corresponds to 4.25 grams. This the value of the oke and it was calculated in modern terms, that is, the weight of the mithqal which is the standard for weighing gold was considered, and it became apparent that one dinar, which is the mithqal, is equal to 4.25 grams. The nisab is twenty mithqals as was stated in the hadith that was transmitted by an-Nasa‘i that, “There is no Zakat on less than twenty mithqals of gold”. It is compulsory to give Zakat on eighty-five grams of gold. That is the calculation. Most of the contemporary scholars have agreed on that.