Zakah is payable on trading stock if their market value is equal to or more than the value of nisaab.
Definition of trading assets
Trading assets are those, which are purchased with the intention of resale or capital gain. Consequently, goods that have been purchased for personal use and not for the purpose of trade are not subject to Zakah, irrespective of their value. Similarly, goods (other than gold and silver) originally bought for personal use are not subject to Zakah if the purchaser subsequently intends to sell them for trade and had not intended it at the time of purchase. Once sold, however, their sale price would be subject to Zakah.