Minimum amount (nisaab) required to pay zakat in dollars

Question

Praise be to Allah.

And it is known that zakat ul-maal (wealth) in
shari’a is required for the two types of
naqd—gold and silver—and what serves their function in
modern times (commonly referred to as cash), whether it is
dollars or riyals or pounds or otherwise.

Nisaab for gold as our Prophet
(peace be upon him) has
informed us (and for currencies made from gold) is 20
mithqaalan, a measure which is equivalent to 85 grams
of pure gold (1 mithqaal = 4.25 grams). It becomes
incumbent upon anyone who owns such an amount in any form to
pay zakat on it in the amount of 2.5%.

Nisaab for silver and currencies made
from silver is 200 dirhams, which is equivalent to 595
grams of pure silver (1 dirham = 2.975 grams).
Likewise, it becomes incumbent upon anyone who owns such an
amount in any form to pay zakat on it in the amount of
2.5%.

It is well known that there is a noticeable
disparity between the value of nisaab for gold and
that of silver in our times. The best and most conservative
for a poor person is to assess how many dollars he has that
have been in his possession for a complete lunar year (Hijri,
which is 354 days). If the amount reaches the value of
nisaab for silver or more, then he should pay from it
for every 1000 dollars, 25 dollars (i.e., 2.5%) to be spent
in the prescribed benficiaries as specified by shari’ah, and
we ask Allah to aid us and help us succeed in haqq il-maal wa
salla allahu ala nabiyyana muhammad