Roman Catechism 18.35

Chapter 18 — Part II: The Sacraments — The Holy Eucharist

Section 35. Quantity Of The Bread — With regard to the first matter of this Sacrament, let this exposition suffice. It is, however, to be observed, that the quantity of the matter to be consecrated is not defined, since we cannot define the exact number of those who can or ought to receive the sacred mysteries.'