Convert from fother [lead] to gros

Unit Definition (fother [lead])
The fother is a traditional English unit of weight for lead. The fother, equal to 30 fotmals, was always a little smaller than a (long) ton. The original version seems to have been equivalent to 2160 avoirdupois pounds, and the version still being used in the nineteenth century was equal to 19.5 hundredweight or 2184 pounds.

Unit Definition (gros)
The gros is a traditional French weight unit equal to 3 deniers (about 3.824 grams).