Answer: One is obligated to eat altogether three “Kezayit”s of Matzah during the Pesach Seder. Every Kezayit amounts to approx. 30 grams of Matzah. Nevertheless, there is room for stringency to eat four or even five “Kezayit”s of Matzah, as we shall now explain.
The Order of the Seder Night
The order for the night of Pesach established by the great and holy Rashi, which we have already discussed, is as follows: Kadesh, Urchatz, Karpas, Yachatz, Magid, Rochtza, Motzi, Matzah, Maror, Korech, Shulchan Orech, Tzafun, Barech, Hallel, Nirtzah.
Three Matzot are placed on top of the Seder plate. Upon reaching the part of the Seder entitled, “Yachatz,” the head of the household takes the middle Matzah and splits it into two pieces. He keeps the smaller of the two pieces and the larger of the two pieces is kept for the “Afikomen.”
The First Kezayit
Upon reaching the part of the Seder entitled, “Motzi-Matzah”, the head of the household takes the three Matzot already prepared on the Seder plate. The top and bottom Matzot are whole and the middle Matzah is the one which was broken in half during “Yachatz.” He holds these Matzot in his hands and proceeds to recite the blessing of “Hamotzi Lechem Min Ha’aretz” followed by the blessing of “Al Achilat Matzah.” It is customary that after one recites the blessing of “Hamotzi,” one lets go of the bottom Matzah and continues to recite “Al Achilat Matzah” while holding only the top whole Matzah and the middle split Matzah. The head of the household must then eat a Kezayit of each Matzah.
Thus far, the head of the household will have already eaten two “Kezayit”s during this part of the Seder. However, the other members of the household, who do not have enough to eat two “Kezayit”s from the Matzot of the head of the household should be given a small piece of the head of the household’s Matzah and he will then supplement that with other Matzot that he has until it reaches the amount of a Kezayit. Regarding the members of the household who do not eat a Kezayit from the head of the household’s Matzot, they do not need to be eating two “Kezayit”s; rather, one Kezayit is sufficient according to all opinions. It turns out that the other members of the household (excluding the head of the household) are only eating one Kezayit at this point in the Seder. Even if the head of the household, for whatever reason, did not eat his allotted two “Kezayit”s and has only eaten one Kezayit, he has fulfilled his obligation. Due to time constraints, we will not be able to elaborate on the reasons behind this law any further.
The Second Kezayit
Afterwards, upon reaching the part of the Seder entitled, “Korech,” one takes a Kezayit from the third Matzah on the Seder plate and wraps a Kezayit of Maror in it and then he dips it in Charoset, after which one recites, “Zecher La’Mikdash Ke’Hillel,” and then eats this while leaning on one’s left side. At this point, the head of the household has eaten three “Kezayit”s of Matzah and the rest of the members of the household have eaten only two “Kezayit”s.
The Third Kezayit
Upon reaching the part of the Seder entitled, “Tzafun,” which is after concluding the festive meal, the Matzah hidden under the tablecloth is eaten as the “Afikomen” and another Kezayit must be eaten from this Matzah. (For the other family members, the Seder leader hands out other Matzot in addition to a small piece of the designated “Afikomen” Matzah.) One must be very careful to eat this Matzah while leaning as well, for if one did not, one has not fulfilled his obligation and will need to eat another Kezayit of Matzah while leaning. This may very well lead to a point of excessive eating which can also be a cause of not fulfilling this Mitzvah, as we have already explained.
Some are stringent to eat two “Kezayit”s during “Tzafun”, one in commemoration of the Pesach offering and one in commemoration of the Matzah that was eaten with it. At this point, the head of the household has eaten five “Kezayit”s of Matzah if he is more stringent, and if not, he has only eaten four. The other members of the household will have eaten four “Kezayit”s if they are more stringent, and if they are not, they will have only eaten three.