The question regarding the minimum amounts (Shiurim) of Matza, Maror, and wine one must consume is a highly controversial and complex topic. Rav Avraham Chaim Naeh in his classic work Shiurim Shel Torah and the Chazon Ish in Kuntress HaShiurim (Chazon Ish Orach Chaim 39) discuss this topic at length. In this essay, we will outline the basics regarding the celebrated controversy whether the Shiurim must be doubled because of the possibility that our eggs are half the size of eggs in the times of the Gemara.
Defining the Size of an Egg
The cup used for the four cups of wine at the seder must minimally contain a Reviit of liquid (see Shulchan Aruch O.C. 472:9). One must consume at least a Kezayit (the volume of an olive) of Matza in order to fulfill the Mitzva (see Rambam Hilchot Chametz U'Matza 6:1 and Shulchan Aruch O.C. 475:1). Similarly, one must eat a Kezayit of Maror to fulfill the Mitzva (see Shulchan Aruch O.C. 475:1 and the sources cited by Rav Shimon Eider Halachot of Pesach 21: note 15).
The Shulchan Aruch (O.C. 486) notes that a Kezayit is the size of half an egg. The Mishna Berura (486:1) notes that the Rambam says that a Kezayit is a third of an egg. The Mishna Berura rules that a sick individual may rely on the opinion of the Rambam. The Mishna Berura (271:68) notes that a Reviit is equivalent to the amount of liquid that one and a half eggs can displace. The Shulchan Aruch (Yoreh Deah 324:1) notes that the minimum amount of flour from which we must take Challa is the equivalent of 43.2 eggs. Accordingly, it is vital to determine the size of an egg.
Students often ask why the Halacha presents its measures in such imprecise terms such as the size of an egg or an olive. The Otzar Hageonim to Eruvin (chapter three) presents a highly insightful answer. The explanation presented is that Hashem knew that the Jewish people would eventually be scattered throughout the world. Thus, had Hashem presented Moshe Rabbeinu with precise measures they would have easily been forgotten with the passage of time. Since eggs and olives are always available throughout the world, Torah measurements can be determined in any environment and culture.
The Chumra of the Tzlach
The Gemara presents two standards for determining the measures mentioned in the Torah. The Gemara in Eruvin (83a) presents the size of an egg as a criterion to determine Torah measurements. In addition, the Gemara in Pesachim (109a) presents thumbs as a criterion to determine Torah measurements. Accordingly, both thumbs and eggs are viable Halachic standards to determine Torah measurements. Indeed, the Shulchan Aruch (Y.D. 324:1) presents both thumbs and eggs as viable options to determine the minimum amount of flour from which Challa must be taken.
Rav Yechezkel Landau, a major eighteenth century authority, in his commentary to the Gemara known as the Tzlach (Pesachim 109a), writes that he carefully measured thumbs and eggs and discovered that the two do not yield equal measurements. In fact, the measurement yielded by thumbs was twice the amount yielded by that of eggs. Rav Landau arrives at an extraordinary conclusion to resolve this problem. He assumes that the size of people's thumbs has not changed since the time of the Talmud. Instead, he concludes that the eggs in his time were half the size of what they were in the time of the Talmud. This ruling has great ramifications. According to Rav Landau, the Kezayit for Matza and other Mitzvot should be regarded as the equivalent of an entire egg and not a half of an egg as had traditionally been assumed. The Reviit should be regarded as the amount of liquid that can be displaced by three eggs instead of an egg and a half as had previously been assumed. The shiur for Challa would now be the volume of 86.4 eggs and not 43.2 eggs as had previously been practiced. In short, Rav Landau ruled that we must eat twice as much Matza as we had been accustomed to consuming in the past in order to fulfill the Mitzva of eating Matza.
Reaction to the Chumra of the Tzlach
Rav Landau's extraordinary ruling was met with both support and criticism. The Vilna Gaon (as reported in the Maaseh Rav 74) agreed with Rav Landau's ruling. The Aruch Hashulchan (Orach Chaim 168:13, O.C. 372:12 and Y.D. 324:5-10) notes that Rav Landau's ruling is adhered to by those who are especially scrupulous in matters of Halacha. However, he notes that most Jews retained the established practice and did not follow Rav Landau's ruling. The Aruch Hashulchan rules that one may choose to follow the strict opinion but he should not impose this Chumra on others. He notes various difficulties with Rav Landau's ruling. First, it constitutes a sharp departure from previously accepted practice. Second, the Gemara in Yoma (80a) teaches that one's mouth can hold an amount of food up to the size of an egg. The Aruch Hashulchan argues that according to Rav Landau one should be able to hold up to the size of two of "today's eggs" in his mouth. The Aruch Hashulchan points out that this is simply impossible. The Aruch Hashulchan also suggests that perhaps Rav Landau used small eggs in his determinations. The Aruch Hashulchan notes that egg size varies from area to area. He points out that this fact was already noted centuries earlier by the Tashbetz (3:33). The Aruch Hashulchan notes that the Mishna (Keilim 17:6) states that the egg that the rabbis speak of is neither a large or small egg but an average one. Accordingly, it is very possible that the eggs in the area of Rav Landau were small and thus skewed Rav Landau's findings.
The Chazon Ish (O.C. 39) defends Rav Landau's ruling. He notes that Shiurim are by definition imprecise and vary depending on the measurement of the great Halachic authorities of the time. Thus, Rav Landau's ruling does not call into question the Halachic practice of prior generations because they relied on the measurements of the rabbis of those generations. The Chazon Ish writes that there is no absolute right or wrong regarding the determination of Shiurim. The Chazon Ish argues that we must accept the Shiurim as determined by the great Halachic authorities, which include Rav Yechezkel Landau and the Vilna Gaon.
The Shaarei Teshuva (O.C. 486) and Mishnah Berura (486:1) adopt a compromising view regarding this issue. They rule that for biblical level obligations we should follow the strict ruling of Rav Landau. Regarding rabbinical level obligations, we may rely on the traditionally accepted smaller Shiurim. Thus, since the first Kezayit of Matza and the Afikoman might be required biblically (see Rashbam Pesachim 119b s.v. Ein Maftirin and Rosh Pesachim 10:34), the larger Shiur of Matza should be consumed for both of these occasions. In addition, by consuming the larger shiur one thereby accommodates the preferred practice of eating two Kezeitim for both the Matza that is eaten at the beginning of the meal and the Afikoman (see Shulchan Aruch 475:1, Mishna Berura 477:1, and Rav Yehoshua Neuwirth cited in Nishmat Avraham 4:68). However, since the Matza eaten for Korech is only a rabbinical requirement, the smaller Shiur suffices. According to Rav Moshe Feinstein, (Kol Dodi 14:11 and 18:3) the Shiur of Matza for Motzi Matza and the Afikoman should be 6.25 by 7 inches and the Matza for Korech need only be 4 by 7 inches (for more sources on this issue see Nishmat Avraham 4:67-70). Since the Mitzva of the four cups is only rabbinical, the smaller Shiur suffices.
According to Rav Moshe Feinstein (Kol Dodi 2:6), 3.3 fluid ounces suffices for the four cups of wine. When the Seder falls on Shabbat eve, the larger Shiur is required since Kiddush is a biblical requirement. According to Rav Moshe Feinstein, the larger Shiur is 4.4 fluid ounces. Since some authorities believe that Kiddush for Yom Tov is always a biblical requirement (see Minchat Chinuch 31), it is best to use the larger Shiur for the first cup at the Seder even if the Seder falls on a weeknight.