K’zayit. Just an Olive?

Rabbi Hadar Margolin

“I had to eat sooo much matzah!”

That’s a response I often get from people when I inquire about their Seder night experience.

Just as many mitzvot have distinct specifications in order to be performed correctly, eating matzah on Pesach has a prescribed time and minimum size requirement. Another obligation of eating matzah, though, is to be joyful as we celebrate
this mitzvah.

One of the most common food-related measurements given by the Torah is the k’zayit—an olive’s volume of a specific food. The commonly accepted minimum obligation with regard to matzah is a fairly large amount that can be difficult to consume and even cause uncomfortable aftereffects—which can make it tough to feel unmitigated joy on yom tov. In some circumstances, the excessive consumption of carbohydrates can even lead to health complications (see; The Diabetics Dilemma page 39).

The reason we have become accustomed to consuming so much matzah is, of course, the presumed halachic size of a k’zayit. Conventional wisdom has come to accept this as quite large and the result is an amount that many people find challenging.

I’d like to present another side to this halacha and offer a perfectly legitimate alternative.

First, how has the commonly presumed halachic k’zayit grown to be so big? The presumed halachic size is based on two assumptions: 1) the k’zayit is the size of half an egg, and 2) the halachic egg is twice the size of today’s common/contemporary egg (see sidebar). Combining these two suppositions, the k’zayit results in the size of a whole egg. Quite large!

The above arguments notwithstanding, there are two compelling reasons to conclude that the k’zayit to be measured against is in fact our contemporary olive:

1. Based on recent scientific evidence, there may be strong reason to believe that the size of the egg has actually not shrunk from earlier periods. The Rambam on the Mishna (Eduyot 1:2) states that a rivi’it of water weighs the same as 27 dirham coins. Thanks to the study of “numismatics” (the science of coins), we now know that the Rambam’s 27 dirham are indeed equivalent to the weight of 1½ eggs—hence the halachic egg can be established to be the same as today’s contemporary egg.

2. Fundamentally, the Chazon Ish (OC 39, 6) maintains that the size of the olive (or the egg, for that matter) during Talmudic times is irrelevant. When Hashem gave the Torah to Moshe at Sinai, he gave a guideline that all measurements of food are defined by a k’zayit, i.e. the size of an olive. Since the original guideline was “the size of an olive,” this guideline remains constant. The Chazon Ish therefore argues that there can be no other logical way to preserve Hashem’s precise
commandment. It is inconceivable
that to determine the correct
measurement we would need to seek an olive from ancient times
to see how it measures up to
today’s olive(s).

Accordingly, when seeking to define the size of a k’zayit, I need look no further than my local olive tree. That, and that alone, is the determining factor. Simply stated: “olive’’ = olive.

While some poskim agree with the larger egg size measurement for the k’zayit, the majority of poskim do not. For those easily able to consume the “large k’zayit” for the biblically mandated mitzvah of matzah (and as codified by the Mishna Brura), great. But it is perfectly legitimate, particularly if one has difficulty consuming this amount, to rely on the smaller, olive size. (For the OU’s recommendations please see “Sizing up the Seder” on page 15.)

Wishing you a fulfilling (not overfilling) and truly joyous Pesach.

Rabbi Hadar Margolin, a Rosh Kollel in Jerusalem is author of a number of Torah volumes including a publication on Halachic Measurements. He can be reached at


• The Talmud (Yoma 80A) states that the beit habliya (the volume of one swallow) equals the size of an egg. Elsewhere (Kritut 14A), the beit habliya is identified as equivalent to the size of two olives.

•  The size of the rivi’it liquid measurements is equal to 1½ eggs. In Pesachim (109A) it states that the rivi’it is the equivalent of 10.8 cubic finger widths. Two hundred and fifty years ago, Rav Yechezkhel Landau of Prague wondered how the egg could possibly be equivalent to the doubly larger finger-based measurement. He concluded that the size of the egg (and olive) must have shrunk since Talmudic times by half. CONSEQUENTLY,

Rabbi Hadar Margolin

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