Halakhah sur Les Nombres 15:20

SEPARATION OF CHALLAH: WHETHER CHALLAH OF THE LAND OF ISRAEL OR CHALLAH OF THE DIASPORA - CONTAINING 5 SECTIONS: It is a positive commandment to separate a contribution from the dough and to give it to priest, as it is said: "the first of your dough you shall contribute [as] a contribution" (Num. 15:20) - and "first" - this does not have a [specific] amount from the Torah - even if one separated [an amount] like a grain of barley has exempted the dough. And one who make all of one's dough challah has done nothing until one leaves over some. And from the words of the Sages, we separate 1/24 of the dough, and a baker who makes [it] to sell in the market separates 1/48. And if the dough becomes ritually impure by accident or compulsion [i.e. forces out of one's control], even the householder separates 1/48.

The commandment of challah (dough-offering): To separate some of our kneading and to give it to the priest, as it is written (Numbers 15:20), "The first of your kneading, set aside challah as a gift." And they, may their memory be blessed, expounded (Eruvin, 93a) [that] "The first of your kneading (arissa)" [means] enough for your measure (issa), and the [dough] measure of the wilderness was an omer, which was one-tenth of an eifah, which is three saah, which is six kav, which is four log, which is six eggs' worth. It turns out that an eifah is four hundred and thirty-two eggs, one-tenth of which is forty-three and 1/5 eggs, and that is the measurement of dough that obligates [the separation] of challah.