When is the nisab of zakat on gold and silver estimated by weight, and when is it estimated by value in the Shafi'i school of thought?

The fundamental principle according to the Shafi'i school is that zakat (definition) on gold or silver is estimated by weight, not by value, provided it reaches the nisab (definition) (threshold) and a full year (hawl) has passed. An exception to this is jewelry intended for trade, which is subject to trade zakat, and its craftsmanship value is considered, or, according to some, it is subject to zakat al-ayn (zakat on the asset itself).

As for used jewelry, if its value and weight differ, such as anklets weighing two hundred [units] but valued at three hundred, the more correct view is that its value is considered. One-quarter of a tenth must be given out as an undivided share. The collector then sells it and distributes its price among the needy, or one may give five minted dirhams whose value is six and a half. It is not permissible to break the jewelry or give gold in its place.

Value is also considered for jewelry used in a forbidden manner, so zakat is obligatory on its value, unlike forbidden utensils, for which their weight is considered. If the jewelry is forbidden in itself, such as an anklet made for a man, then its weight is considered, not its value. However, if it is forbidden due to an external factor (such as if it was made for a woman and used by a man), then its value is considered.