The mitzvot of the Seder require that Matzah and Maror be “eaten” in
appropriate quantities and not just nibbled. The minimum requirement
for eating a food, as taught by the Rabbis of the Talmud, is a “Czayit”
(=size of an olive). This must be eaten preferably within 4 minutes but if
necessary in up to 7 minutes. A “Czayit” is approximately the size of 1
fluid oz or 29 cubic centimeters of water. The weight of 29cm3 of water
is 29grams. Therefore most of the guides (including earlier editions of
the Kashrut Authority Pesach Handbook) state that a “Czayit” of matzah
is 1oz or 29grams of matzah. However according to most opinions this
is incorrect.

In general all Torah measurements are established by volume
rather than by weight. Therefore one “Czayit” of matzah is equivalent
to the amount of matzah that takes up the ‘volume’ of 29 grams of
water or 29ml. In reality the ratio of volume to weight of matzah
compared to water is no more than 2/3. This means that the Shiur
of a “Czayit” for the fulfillment of biblical mitzvot is approximately 19
grams of matzah, (not 29 grams) which is approximately 1/3 of a hand
made shmurah matzah or 2/3 of a machine matzah. This amount is
considerably less than the usually recommended amounts.
Furthermore, the requirement for a “Czayit” for a Rabbinic Mitzvah is
only 2/3 the above measure. Therefore a “Rabbinic Czayit” is only 13
grams of matzah.

Therefore for Korach (the sandwich) all that is required is one
rabbinic “Czayit” a quarter of a Shmurah Matzah or half a machine
matzah. When eating the customary two “Czaytim” for Afikoman
all that is required to be eaten is 26 grams of matzah (2 rabbinic
“Czaytim”) i.e; 1/2 a shmurah matzah or 1 machine matzah. Similar
measurements apply to maror.
The above information allows us to ascertain the appropriate
requirements of matzah and marror with realistic amounts, able to be
consumed relatively easily by all the seder participants.