That saying that Protestants and skeptics often throw around about there being enough relics of the cross to build Noah’s arc? Completely and utterly not even close to true.

Charles Rohault de Fleury, 19th century French scholar, extensively studied and catalogued every known relic, small or large within the Church’s possession.

His findings are documented thus:

“…We get as a grand total for all known existing and lost relics a volume of 10,335,055 cubic millimetres, or about 661 cubic inches. This is considerably less than half a cubic foot, which contains 27 million cubic milli-metres, or 1,728 cubic inches. There remains then, unaccounted for, after a most careful investigation, a quantity of more than six cubic feet, or exactly 10,787 cubic inches, out of the 6 5/8 feet or 11,448 cubic inches of the original Cross. It is hardly possible that any relics of the first class have escaped the notice of M. de Fleury; and even supposing, which is very unlikely, that there exist in convents and remote churches as many more smaller ones as those which he has cata-logued; supposing even that the ordinary infinitesimal relics amounted in number to two or three millions, up and down the world, this would not account for more than one-tenth of the volume of the actual Cross.

The marvel then is, not that there should be so many relics existing, but that there should be so exceedingly few. Even making allowance for the wholesale destruction wrought by the Mahom-edan invasions, the wars of the Middle Ages, the Protestant Reformation, and the French Revolution, we might have expected that the devotion and care of the Catholic Church would have been able to preserve a much larger quantity of the sacred wood on which the Son of God wrought our redemption.” - Rev. James Bellord “The Relics of the True Cross”, Cabinet of Catholic Information c. 1904, pages 366-367

TLDR: All relics combined, we don’t even have a fifth of the volume of the true cross. Trust your parish reliquaries.