Many of the mitzvos special to Seder Night involve eating or drinking. These are the mitzvos of the Four Cups, Matzah, Marror, Korech, and Afikoman. An important part of Seder Night is knowing how much we need to eat or drink for each of these mitzvos, and the time frame in which we must be eat.

In this article we will present a guide to the correct amount that one should eat or drink, and the respective time frames. In particular, we will focus on the amount known as a kezayis, which is the basic unit for most eating-related mitzvos.

As we will see, determining the amount of a kezayis, which literally means the volume of an olive, is not as simple as it might at first seem.

An Olive as Half an Egg?

The mitzvos of Seder Night that require eating all require that we eat a shiur – amount – of a kezayis.

The exception to this is Karpas (Shulchan Aruch, Orach Chaim 573:6), which does not require a kezayis because there is no obligation of halachic eating, but only to make a change from the ordinary, prompting children to ask why this night is different. (One should eat less than a kezayis of Karpas in order to avoid the need to recite a brocho acharonoh.)

The smallest amount of food that is considered eating in halacha is a kezayis (see Toras Kohanim 12:2). A kezayis is a measure of volume, and is unrelated to weight (Rambam, Commentary to Mishnah, Taharos 3:4; Chazon Ish 39:17). The Mishnah states that it refers to the size of an average olive (Keilim 17:8).

Determining the amount of a kezayis would appear to be fairly simple: It is the volume of an average olive. Yet, the Rishonim clarify that this is not as simple as we might think.

The Gemara (Yoma 80a) writes that a person can swallow the volume of an egg at one time. In addition to this, the Gemara elsewhere (Kerisus 14a) states that a person can swallow up to two kezayis amounts at one time.  Tosfos (Eiruvin 80b; Yoma 80a) infers from this that the volume of an egg is twice the volume of an olive, so that an olive – a kezayis – equals half an egg (see also Magen Avraham 486).

Today’s olives are approximately one-ninth the volume of today’s eggs – far less than one-half (see Sefer Kezayis p. 24). Since olives were clearly far bigger (at least relative to eggs) in the times of Tosafos, it appears that (according to Tosafos) we cannot determine the size of a kezayis using today’s olives as a measure – unless we assume that the halachic amount decreases with the decline in the size of olives.

The historical decline in the size of olives emerges from the conclusion of Tosafos. According to the Rambam, however, there is no proof that our olives are any different to those of earlier times.

The Rambam does not explicitly discuss the size of a kezayis, but it can be inferred from his rulings concerning the size of a halachic meal (this is especially relevant for purposes of an Eruv). According to the Rambam’s rulings, the volume of bread for two meals is six eggs, which is equivalent to the volume of eighteen dried figs (Laws of Eiruvin 1:9; based on the Mishnah, Eiruvin 82b, and Gemara Eiruvin 80b; This equivalence is disputed by Tosafos.). The volume of a dried fig is thus one third of the volume of an egg.

We know from the Gemara elsewhere (Shabbos 91a) that that an olive is smaller than a dried fig (this is clearly true for our olives). According to the Rambam, it thus follows that a kezayis is less than one third of an egg.

In fact, according to the Rambam a kezayis might be far smaller than one third of an egg, and this is what we would conclude based on today’s olives. However, out of doubt, the Rambam’s opinion is generally referred to as being one third of the volume of an egg, and this is the amount one must eat (according to the Rambam) to ensure that a kezayis is consumed.

The Size of an Egg: A Great Decline

In actually determining the volume of an egg, the simplest way is to use the displacement method: Place an egg into a full container of water, and measure the volume of water displaced.

This is in fact the method that the Shulchan Aruch recommends (Orach Chaim 456:1; see Yoreh De’ah 324:1).

A second, more elaborate method is based on the relationship of an egg to a revi’is – a halachic measure of volume specific to liquids. A revi’is is the volume of one and a half eggs; in other words an egg is two-thirds the volume of a revi’is (Rambam, Laws of Mikvaos 6:13).

The Gemara (Pesachim 109a) states that a revi’is is the size of a container measuring two fingerbreadths by two fingerbreadths by 2.7 fingerbreadths, where each fingerbreadth is the width of an average person’s thumb measured at the joint or at the widest part of the thumb near the joint (see Daas Torah, Treifos 38:115; Shut Iggros Moshe, Orach Chaim 1:136; Mishnah Berurah 11:19). Two-thirds of this volume is the volume of an egg.

One great complication in the kezayis issue arose when the Tzelach (Pesachim 116b) compared these two calculations. He figured the average thumb-width to be 2.55 cm (1 inch) and, using the above formula, the result came to approximately 120 cc (4.1 fluid oz.).  He also measured eggs using the water displacement method above, and found that they measured slightly less than 58 cc (2 fluid oz.). In other words, the volume of actual eggs was just under half the volume of the thumb-measurement egg!

The Tzelach therefore reasoned that one of two things must have happened. Either people’s thumbs are larger than they had been in the time of the Gemara (so that his actual egg measurement was correct while his thumb-measurement was too large), or eggs grew smaller in size than they had been in the time of the Gemara (so that his thumb-measurement was correct while his egg measurement was too small).

In deciding between these two options, the Tzelach makes the following assumption: “It is well known that succeeding generations diminish, and do not increase.” It follows that the change must be in the eggs. Thus he coins the famous expression niskatnu habaitzim (eggs have decreased in size).If the size of athumb remained the same, the size of eggs diminished by one-half since the time of the Gemara.

Accordingly, thumb measurements are the more accurate method for calculating the true baitza, and all shiurim dependent on the size of eggs, including the revi’is (one and a half eggs), the kebeitza(one egg), and the kezayis (one-half or one-third of an egg), must be measured with thumb-measurements.  Should they be measured with present-day eggs, the volume must be doubled. For example, a revi’is, which the Gemara states is the volume of 1.5 eggs, is actually the volume of three present-day eggs.

In fact, the Tashbatz (3:33) already preceded the Tzelach, and stated that thumb-measurements are much larger than egg-measurements, so that “it is fitting to be stringent concerning Torah mitzvos.”

Dissent on the Decline of Eggs

Many authorities have disagreed with the Tzelach’s assertion. This clearly emerges from those authorities who advise to measure the volume of an egg by displacement of today’s eggs (Shulchan Aruch 456:1; Magen Avraham 210:2; Shulchan Aruch HaRav 456:1; see also Aruch HaShulchan, Orach Chaim 168:13 and Yoreh De’ah 324:5), and it is stated explicitly by several Poskim.

In Shaalos U’teshuvos Teshuva Me’ahava (no. 324) the author – a disciple of the Tzelach – argues that the Tzelach used his own thumb, which was actually far larger than the average thumb, as a measure. (Now, as well most people’s thumb measures about two centimeters.) This resulted in an overly large thumb-measurement. This was also the opinion of Rav Chaim No’eh. The Aruch HaShulchan (Yoreh De’ah 324:6) takes the opposite approach, namely that the eggs in the Tzelach’s area were smaller than average.

Rav Dovid Feinstein (Haggadah Kol Dodi 2:5) suggests that the size of eggs remained constant, while thumbs actually grew – contrary to the Tzelach’s assertion that “succeeding generations diminish.” According to this approach, one may of course use the present-day egg measurement, for it is the thumb-measurement that is now inaccurate. Rav Dovid Feinstein does not reject the Tzelach, but only explains a possible rationale of those who do.

Finally, some Poskim writes that even if eggs or olives diminished in size since the time of the Gemara, this does not affect the shiur of a kebeitza or kezayis. This is because amounts based on eggs or olives depend on the eggs or olives of each generation and are not a fixed amount (Shut Beis Shlomo, Orach Chaim 107; Shut Beis Yitzchak, Yoreh De’ah 2:133; Shut Chasam Sofer Orach Chaim 181; Shiurei Torah 5:1 from Chesed LeAvraham; Shut Iggros Moshe, Yoreh De’ah 3:61 and Orach Chaim 1:136).

According to this approach, one should use present-day eggs and olives to measure the relevant shiur, even if the result does not concur with that of thumb-measurements. Rav Chaim No’eh writes in many places that the common custom in Europe was to rely on these amounts, and not to follow the stringency of the Tzelach (though the Steipler has written that the custom was specifically to follow the Tzelach’s stringency).

On the other hand, some Poskim agree with the Tzlach’s ruling (see Maaseh Rav 105 and 74; Shaarei Rachamim (nos. 62 and 165); Rosh Efraim 3:16; Maharam Schick, Yoreh De’ah 199). As we will see below, many contemporary authorities rule that one must take his opinion into account, especially for Torah mitzvos.

Contemporary Rulings

To summarize, two main issues must be resolved in determining the amountof a kezayis: 1. Whether a kezayis is one-half or one-third of an egg; 2. Whether a kezayis should be measured with present-day eggs or with thumb-measurements.

Most authorities rule that for Torah mitzvos, one should eat an amount equal to half an egg (in line with Tosafos), whereas for a rabbinic mitzvah one may eat an amount equal to a third of an egg (see Shulchan Aruch HaRav, Aruch HaShulchan and Mishnah Berurah, all 486:1).

The Mishnah Berurah adds that for a rabbinic mitzvah that requires a brachah, such as Maror, one should be stringent and eat an amount equal to half an egg. Some (such as the Mishnah Berurah and Aruch HaShulchan) add that where it is not difficult, one should eat an amount equal to half an egg even for rabbinic mitzvos.

As for using today’s eggs or thumb-measurements, the Mishnah Berurah rules thatfor Torah mitzvosone should use the larger thumb-measurement sizes (the Tzelach’s stringency), whereas for rabbinic mitzvos one can rely on present-day eggs (486:1; Biur Halachah 271:13; the Mishnah Berurah finds the Tzelach’s stringency difficult because of the measure of a melo lugmav).

The Chazon Ish (39:8 and 17), however,ruled that for all shiurim, including the kezayis, one should follow the Tzelach. However, the Chazon Ish applied the ruling as stringency, since in principle he maintained that the basic shiur depends on the average olive of each generation (Shiurin shel Torah 11).

Rav Chaim Kanievski testifies that the Chazon Ish actually used this amount for rabbinic mitzvos, eating an amount of one-third of a present-day egg (which equals 17 cc – still considerably larger than a present-day olive; see letter printed in Mikraei Kodesh (Harari), p. 572, concerning Maror; see also Kezayis Hashalem, Chap. 11 ). However, for a revi’is (the Four Cups) the Chazon Ish used the thumb-measurement volume.

Rav Chaim No’eh maintains that there is no discrepancy between the volume of a present-day egg and that of thumb-measurements.

There is of course far more to be written concerning the different opinions on shiurim, and much research has been conducted in recent years involving such matters as the weight of ancient coins (due to the Rambam’s reference to the Egyptian Dirham), the size of a Mikvah, and much besides. For more information, the reader is referred to Rabbi Dovid Braunfeld’s Moznei Tzeddek, from which much of the material above is adduced.

We will continue to the practical guidelines for Seder Night.

Actual Shiurim

Based on the foregoing analysis, we know that the measures of an etzbah (fingerbreadth), revi’is, kebeitzah and kezayis are all interrelated. We also know that an amah (cubit) equals six tefachim (Eiruv 13b), which in turn equal 24 etzba’os (Bechoros 39b), so that even the amah and tefach are interrelated with the other shiurim.

The Chazon Ish based his measurements on the amah. He writes (39:8) that the shiur of an amah used in Europe was 22.8 inches (58 cm; note that this is considerably longer than the length from a person’s elbow to the tip of his middle finger; see Rashi on Kesubos 8b and Menachos 11a).

Based on an amah of 58 cm, a revi’is will be 5.1 fluid oz. (150 cc; see Shiurin shel Torah, Mitzvos 18). An egg without its shell is3.0 fluid oz. (90 cc), and a kezayis is one-half or one-third of this. The volume of the egg is approximately twice that of present-day eggs. From this the Chazon Ish concluded that the halachah follows the stringency of the Tzelach.

However, the measures given by Rav Chaim No’eh were used for many centuries in Sefardic communities (see Shut Or LeZion Vol. 3, no. 3, sec. 4; Yecheveh Daas 4:58), and it was also the long-established minhag Yerushalayim (see Introduction to Shiurin shel Torah; see Biur Halachah 271:13 concerning the custom outside Israel). When the Chazon Ish introduced his shiurim (based on the Tzelach), Rav Chaim No’eh defended the older custom with a series of books, so that the shiurim thus became known as Rav Chaim No’eh’s shiurim.

These shiurim were based on the revi’is, which the Rambam writes contains the volume of water displaced by 27 Dirhams (Commentary to Mishnah, Edios 1:2). The Dirham is an Arabic coin which has been in use in Middle Eastern countries from the times of the Geonim (the early Middle Ages), and which continues to be in use in some countries today. The weight of the water displaced by one Dirham is 3.205 grams. A revi’is of water (27 Dirhams) thus weighs 86 grams, and its volume is 86 cc (2.9 fluid oz.).

A revi’is is thus a volume of 86 cc (Shiurei Torah 3:6), so that the volume of the various kebeitzasincluding the shell is 1.95 fluid oz. (57.6 cc) and without the shell1.82 fluid oz. (53.8 cc). A half-egg kezayis is therefore 0.87 fluid oz. (25.6 cc; Shiurei Torah 3:12), and third-of-an-egg kezayis is 0.58 fluid oz. (17.3 cc). Concerning matzah, Rav No’eh advises that one should eat 0.97 fluid oz. (28.8 cc), to account for matzah particles that remain stuck between the teeth.

These measures correspond well with the volume of present-day eggs.

Rav Dovid Feinstein calculated the measurements based on both present-day eggs and thumb-measurements. His measures for actual eggs are very close to the shiurim given by Rav Chaim No’eh. Based on fingerbreadths (which he based on Rav Moshe Feinstein’s amah), a revi’is was calculated as 4.42 fluid oz. (131cc), an egg as 2.94 fluid oz. (87 cc), and one-half and one-third of an egg as 1.5 fluid oz. (44 cc)and 0.98 fluid oz. (29 cc), respectively.

The following are thus the mitzvah measurements.


This is a Torah mitzvah, and the Mishnah Berurah writes that one should therefore follow the stringencies of both the Tzelach (thumb-measurements) and Tosfos (half an egg). The largest thumb-measurement size for an egg is that of the Chazon Ish (3.38 fluid oz. or 100 cc). A kezayis is half of this, which amounts to 1.69 fl. oz. (50 cc). Note that according to the Chazon Ish, the shiur is one-third of an egg, which is 33cc. As noted above, according to Rav Chaim No’eh the shiur is 0.87 fl. oz. (25.6 cc), though he advised eating 0.97 fluid oz. (28.8 cc) to account for matzah that might get stuck between teeth.

Although the Shulchan Aruch states that one who is eating from the three matzos on ke’ara should eat two kezaysim (475:1), for this halachah a kezayis of one-third a present-day egg is sufficient, so that the large kezayis noted above is sufficient to fulfill this, too.


Korech is a rabbinic mitzvah, fulfilled by eating a kezayis of maror and a kezayis of matzah together. One can therefore use the smaller shiur of a kezayis, meaning one third of a present-day egg. The largest contemporary opinion for this shiur is that of Rav Chaim No’eh, amounting to 0.65 fl. oz. (19.3 cc).

According to some authorities one should use half-egg kezayisim even for a rabbinic mitzvah, which will amount to 0.97 fl. oz. (28.8 cc).


One should preferably eat two kezaysim for Afikoman (see Mishnah Berurah 477:1). Since this is a rabbinic mitzvah, one may use the small kezayis of one third of a present-day egg, so that two such kezaysim total 1.28 fl. oz. (37.8 cc).  According to the basic halacha, one need only eat one kezayis (Shulchan Aruch 477:1): 0.65 fluid ounces (19.3 cc).


The basic shiur is equivalent to that of Korech. However, the Mishnah Berurah rules (as noted above)that because a berachah is recited, one should use a half-egg kezayis of 0.97 fl. oz. (28.8 cc).

Note that the easiest way to actually measure the matzah and other shiurim is by  weight. For hand matzah, the largest shiur is approximately 29g of matzah, and the smallest shiur is 11.2g. For machine matzah (which has a different density) the amounts are 31.0g and 12.0g, respectively (amounts taken from Moznei Tzedek).

Four Cups

The Mishnah Berurah (Biur Halachah 271:13) rules that because the mitzvah of Four Cups is rabbinic, one can rely on the smaller shiur, which amounts to 86cc. However, when Pesach falls on Shabbos (as this year), the first of the Four Cups is also used for Kiddush, which is a Torah mitzvah. The Mishnah Berurah rulesthat this Cup thus requires the larger volume 5.1 fluid oz. (150 cc).

According to the Chazon Ish, one should use this larger volume for all cups.

We want to wish everyone an enjoyable and kosher Pessach

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2 Responses to “Seder Night Shiurim”

  1. What is the density of lettuce?

    • Please explain yourself.

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