How Much To Eat On Pesach-from OU website

Kezayit Matzah
There are some variances amongst halachic authorities as far as how the precise measurement should be calculated, but the minimally recommended size is approximately 26 cubic centimeters .
Although strictly speaking, the Torah level mitzvah of matzah requires one to eat the measurement of a single kezayit, there is a rabbinic requirement to consume a total of five kezeitimat different intervals of the seder.
The first two portions are eaten together, one associated with the benediction of hamotzi with the other associated with the benediction of al achilat matzah.
The third kezayit is eaten as part of the traditional korech sandwich from the sage, Hillel, which serves as a reminder of the Beit Hamikdash. The fourth and fifth kezeitim are eaten together at the end of the festive meal as part of the Afikoman.
The fourth kezayit is associated with the korban Pesach, while the fifth kezayit is a reminder of the chagigah offering that was brought during the Three Festivals. Ideally, the required measurement for the additional four kezeitim should be the same as the basic mitzvah of matzahmentioned above. However, since these four kezeitimare rabbinic requirements, in an extenuating circumstance there is room for leniency to eat less.

Kezayit Moror
Nowadays, with the absence of the Beit Hamikdash (Holy Temple), the korban Pesach (paschal lamb) is not brought and therefore its interdependent sister mitzvah, maror (bitter herb), is not a Torah-level precept, but is currently a rabbinic ordinance. This is because our Sages mandated that one must still eat the traditional bitter herb independently.
Therefore while the minimal amount of maror that one is required to consume at the seder is also a kezayit, there are some variances amongst halachic authorities as far as how this measurement should be calculated. Moreover, some authorities calculate the measurement diferently for mitzvot derabbanan.
The minimal size given is approximately 26 cubic centimeters, which can be limited to just a single, large leaf of romaine lettuce .
Medium or small leaves of romaine lettuce will respectively amount to approximately three-fifths or one-fifth of the required amount. Large romaine stalks are approximately half a kezayit, while small romaine stalks are roughly one-quarter’s worth. A single endive is between one half to one quarter of the required amount, depending upon whether the leaf is large, medium, or small. A filled one ounce shot glass of ground horseradish constitutes a kezayit.

Revi’it Wine
The requirement of drinking four cups of wine is rabbinic in nature and the minimal measurement required for the four cups is a rivi’it for each cup. There are some variances amongst halachic authorities as far as how this measurement should be calculated, but the minimal size given is approximately three ounces . It should be noted that if one’s cup holds more than a rivi’it, one should try to drink the entire cup or at least most of it.

Passover is a time when we became a nation and is therefore an opportunity to appreciate the many laws that were given to us. As we celebrate our freedom during the Passover holiday, we have the opportunity to reflect on what makes our heritage so unique. The meticulousness, care, and detail with which we approach ritual observance will certainly make our heritage special.