No big deal; there was a forest full of that wood bought and sold in the middle ages.
A ‘forest’ which was rigorously measured in the 19th century.
The total volume of known cross splinters amounts to 0.004 cubic meters.
**(op. cit., 97-179). Here is the calculation of this savant[Rohault de Fleury]: Supposing the Cross to have been of pine-wood, as is believed by the savants who have made a special study of the subject, and giving it a weight of about seventy-five kilograms, we find that the volume of this Cross was 178,000,000 cubic millimetres. Now the total known volume of the True Cross, according to the finding of M. Rohault de Fleury, amounts to above 4,000,000 cubic millimetres, allowing the missing part to be as big as we will, the lost parts or the parts the existence of which has been overlooked, we still find ourselves far short of 178,000,000 cubic millimetres, which should make up the True Cross.**
http://www.johnsanidopoulos.com/2011/09/distribution-of-pieces-of-true-cross.html