Digressions on wine barrels and IMO tonnage conventions
Due to the similarity of pronunciation, the former barrel of wine has remained a ton to this day, but in the case of vessels it is not a measure of mass but a unit calculated on the basis of volume. The weight of wine transported in a thirteenth century barrel was probably around 1015-1150 kg and was close to “our modern ton” used as a unit of mass. Later, from the 15th century until 1835, the concept of “ton” was even more similar to the modern ton because it meant a mass of about 1015 kg, i.e. it differed by only 15 kg from the current ton, as a unit of mass.
More digressions on this subject on polska-morska.pl.