What is the amount of zakat due on 20 sacks of dates?

The Nisab (minimum amount) for what is produced from the land is five Wasqs, which is equal to three hundred Sa's, approximately 900 kilograms. One-tenth (Ushr) must be given for what is irrigated without cost, and one-half of one-tenth (half-Ushr) for what is irrigated with cost. If the aforementioned dates reach the Nisab or more, and their irrigation was without cost, then one-tenth is obligatory. If their irrigation was with cost, then one-half of one-tenth is due.