The following is a guideline as to how much matzah, wine and maror must be consumed at the seder.
Without going into much detail, we are stricter if the mitzvah is a Biblical mitzvah as opposed to a Rabbinic mitzvah. Based on the following facts that an average machine-made matzah is 60 cubic centimeters and an average hand-made matzah (7 ½ matzot to a pound) is 120 cubic centimeters, the following amount of matzah need to be consumed for the following mitzvot:
- Motzi matzah: A total of 4/5 of a machine-made matzah or 2/5 of a hand-made matzah
- If one is eating the motzi matzah from the top & middle matzot, then:
- Machine-made matzah: At least 1/3 of a machine-made matzah must be taken from each of the top & middle matzot, but the total must be equivalent to 4/5 of a machine-made matzah
- Hand-made matzah: At least 1/6 of a hand-made matzah must be taken from each of the top & middle matzot, but the total must be 2/5 of a hand-made matzah
- Note that the aforementioned amounts are based on a number of stringencies. As such, if eating this much matzah will hinder your simchat Yom Tov (enjoyment of Yom Tov), then you may satisfy your obligation of motzi matzah with 2/5 of a machine-made matzah or 1/5 of a hand-made matzah.
2. Koreikh: A total of 1/3 of a machine-made matzah or 1/6 of a hand-made matzah
3. Afikoman: The basic halakhah is that only one kzayit (size of an olive) must be eaten, which would be 1/3 of a machine-made matzah or 1/6 of a hand-made matzah, but the custom is to have two kzeitim, so, if possible, one should have 2/3 of a machine-made matzah or 1/3 of a hand-made matzah
All of these amounts are based upon the premise that the "kzayit" requirement is a requirement of a kzayit from the time of the mishnah which is different than the current size of an olive. Someone who is ill and cannot digest that much matzah may rely on the more lenient view that the requirement of a kzayit for each of motzi matzah, koreikh and afikoman is the current size of an olive, which is approximately 7.5 cubic centimeters, which is 1/8 of a machine-made matzah or 1/16 of a hand-made matzah.
Regarding how much wine/grape juice must be drunk, the cup must be at least a "revi'it," which is at least 3 fluid ounces and one must drink at least a majority of the cup. If this is too difficult, then one may rely on the position that no matter how large the cup is, one only needs to drink a majority of a "revi'it" and he can rely on the position that a "revi'it" is only 2.5 fluid ounces and drink a majority of that amount, which is 1.25 fluid ounces.
Regarding how much maror must be eaten for maror or koraikh:
If you are using pure, grated horseradish, then you must eat an amount that can be compacted into a vessel measuring .7 fluid ounces.
If you are using whole leaf Romaine lettuce, then you must eat enough leaves to cover an area of 8 by 10 inches.
If you are using Romaine lettuce stalks only, then you must eat enough stalks to cover an area of 3 by 5 inches.