How is the zakat threshold for trade goods calculated given the differing values of gold and silver?

Scholars differed concerning the valuation of trade goods. The majority held that they should be valued by what is most beneficial to the poor (i.e., by gold or silver, whichever reaches the nisab and is more advantageous for the poor). Some scholars were of the opinion that the valuation should be based on the currency with which they were purchased, or the predominant currency in the country. As for the Malikis, they considered the valuation of each type of good according to what it is most commonly sold for. The most preponderant opinion is that of the majority, which is to value them by what is most beneficial to the poor, and in this matter, that is valuation by silver.