First: Zakah is Due on Olives
According to the Hanafites, the Malikites, the early statement of Ash-Shafi`e, and one narration of the Hanbalites, Zakah is due on olives because its produce can be stored away for future usage. Please refer to [Al-Hawi, vol.3/pp.505-506] by Al-Mawardi.
Second: The Nisaab of Olives Zakah
The Nisaab of olives Zakah is five Awsuq according to the opinion of the majority of the Muslim scholars, contrary to Abu Hanifa`s opinion as regards the Nisaab of crops and fruits. If the amount of olives was less than five Awsuq, then no Zakah is due on it, but if it was five or more, then Zakah is due on it, as indicated by the following Hadith: The Prophet (PBUH) said: "There is no Zakat on less than five Awsuq (of dates), or on less than five camels, or on less than five Awaq of silver." (22 Yemeni Riyals Faransa)" [Agreed upon].
According to modern weights and measurements, the Nisaab of olives Zakah is (611kgs.), as stated in the book, [Al-Maqadeer Ash-Shar`iah (pp.201] by Al-Kurdi. Here, what counts is the weight of the olives, not the oil.
Third: The Amount of the Zakah Due on Olives
On the land irrigated by rain water, Ushr (i.e. one-tenth)is compulsory as Zakah; and on the land irrigated by the well, half an Ushr (i.e. one tenth)is compulsory as Zakah paid by the owner, whether the yield was olives, or olive oil. This is indicated by the Hadith of the Prophet (PBUH) who said: "On a land irrigated by rain water or by natural water channels or if the land is wet due to a nearby water channel Ushr (i.e. one-tenth) is compulsory (as Zakat); and on the land irrigated by the well, half of an Ushr (i.e. one-twentieth) is compulsory (as Zakat on the yield of the land)." [Bukhari].
Fourth: It is preferable that Olives Zakah is Given as Oil
Ash-Shafi`e (May Allah bless him) said, "It is permissible to give olives as Zakah, but it is preferable to give one Ushr as oil."
Kindly refer to the book: [Al-Majmou`] by An-Nawawi.
Fifth: Olives Zakah is to be Given by the Owner if he Sold the Fruits while on the Tree
It is impermissible to sell the olives while on the trees, save if they are obviously ripe. In this case, the Zakah is due on the owner alone, because the Zakah becomes due when the olives are ripe, and they were while in his possession. Please refer to [Moghni Al-Mohtajj, vol.4/pp.461]. However, if the owner sold the olives after they had become obviously ripe, then it is obligatory that he exclude the amount of Zakah from that deal, or to notify the purchaser in order to avoid dispute.
Sixth: Ruling on Exchanging Olives with Olive Oil
It is impermissible to exchange olives with olive oil; rather, it should take the form of sell and buy transaction in order to avoid usury (Riba). This is because olives are the origin of olive oil, and it is impermissible to exchange two items of the same kind. Please refer to [Al-Mohazab, vol.2/pp.37] by Ash-Shirazi and [Al-Hawee, vol.5/pp.243] by Al-Mawardi.
Seventh: It is preferable to give Zakah from the same kind on which Zakah is due. However, it is permissible to give the Zakah in cash to facilitate for the recipients and to achieve that, which is best to the poor, as indicated by the Hanafites Mazhab (Juristic school). Please refer to [Al-Ikhtiar Li`ta`leel Al-Mokhtar, vol.1/pp.102].
Eighth: The Costs of Pressing Olive Oil aren`t Deducted from its Zakah
Costs of processing the olive oil aren`t to be deducted from the Zakah due on it; rather, the Zakah should be given from the overall yield. Please refer to [Moghni Al-Mohtajj, vol.4/pp.461] by Ash-Shirbini. The proof of this is that the Islamic Sharia has differentiated the amount of the due Zakah on basis of the irrigation costs; therefore, it prescribed an Ushr (one-tenth) in case the costs of irrigation were paid by the farmer. Had all the costs of cultivation been deducted, there wouldn`t have been such a variation in the amount of the obligatory Zakah. Accordingly, the farmer either gives the Zakah from the olives yield before pressing, or from the net olive oil after pressing, and the cost of pressing the olives isn`t to be deducted from the due Zakah. And Allah Knows Best.