The nisab is the value of about 85 grams of gold or 595 grams of silver; wealth at or above this level, held for a lunar year, is subject to zakat. Many scholars advise using the silver nisab as it benefits more of the poor.
References
No specific citation was provided for this answer. Verify with a qualified scholar and the primary sources.
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.