How Much is a K’zayit of Bread?

How much is a k’zayit of bread?

As the term suggests, a k’zayith is a volume equivalent to the size of an average olive.
The type of olive referred to by Hazal is the strain known as ‘Ssuri’ or ‘Ssori’. This is the conclusion of Prof. Mord’khai Kislev of Bar-Ilan University, an internationally renowned expert in the fields of archeology, botany and agriculture, in an exhaustive study on the subject. Prof. Kislev points out that there are approximately 70 olive trees in Israel that are 1700-2000 years old, and 7 that are approximately 3000 years old. The overwhelming majority of these trees are of the Ssori strain and continue to produce olives identical to the olives produced by similar trees 30 years old.
The volume of this type of olive is 2.5-3.5 cc. The average volume of this type of olive, therfore, is 3cc. – an amount that would fill a teaspoon. If one wishes to assume, without basis, that the average olive referred to by Hazal is of the Nabali strain – the other major type of olive common in Eress Yisrael – the figure would be 5 cc. There is no reason to accept such a claim; 3 cc is the correct figure.
These amounts are exactly what a normal person would imagine a k’zayith to be (assuming they were not first bamboozled by irrational claims to the effect that olives were once much larger and that therefore the volume of an olive is really the volume of an egg).
Rabbi David Bar-Hayim