How is zakat calculated on a sum in euros for someone living outside the Eurozone, and is zakat due on the entire amount that has been held for a year, or on the difference between it and the nisab?

If the wealth reaches the zakat threshold (nisab), which is equivalent to 85 grams of gold or 595 grams of silver, and a full lunar year passes over it without its value dropping below the nisab, then its zakat becomes obligatory by disbursing a quarter of a tenth (2.5%) of the entire wealth. It is permissible to pay the zakat on euros in dinars or any other currency.