Brachos 7:2-3

Brachos 7:2

Women, slaves and minors do not participate in a zimmun. The minimum quantity necessary to participate in a zimmun is an olive-sized portion; Rabbi Yehuda says an egg-sized portion.

Brachos 7:3

For a zimmun of three, the leaders says “nevarech” (“let us bless”); if it’s three plus the leader, he says “barchu” (“bless”). For ten, he says “nevarech l’Elokeinu” (“let us bless our G-d"); for ten plus him, he says “barchu.” This stays the same no matter how large the group gets (according to Rabbi Akiva). For 100, “nevarech laShem Elokeinu” (“let us bless Hashem, our G-d"); for 100 plus him, “barchu.” For 1,000, “nevarech laShem Elokeinu, Elokei Yisroel” (“let us bless Hashem, our G-d, the G-d of Israel"); for 1,000 plus him, “barchu.” For 10,000, “nevarech laShem Elokeinu, Elokei Yisroel, Elokei tzvakos yosheiv hakruvim al hamazon she’achalnu” (“let us bless Hashem, our G-d, the G-d of Israel, the G-d of Hosts, seated above the cherubim, for the food we have eaten”); for 10,000 plus him, “barchu.” Whatever text the leader uses, the rest respond accordingly. Rabbi Yossi HaGlili says we change the text based on the size of the group as per Psalms 68:27, “Bless Hashem in assemblies….” Rabbi Akiva says this in inconsistent with what we do in shul, where we always say “barchu es Hashem” (“bless God”) no matter how many are present. Rabbi Yishmael clarifies that we actually say “barchu es Hashem hamevorach” (“bless God, Who is blessed”).