Convert from libra [Portugal, Spain] to fother [lead]

Unit Definition (libra [Portugal, Spain])
The libra [Portugal, Spain] a traditional unit of weight. The libra was the Roman unit from which the English pound is descended; the symbol "lb" for the pound comes from this unit. The Spanish and Portuguese units are larger, generally in the range from 1.011 to 1.016 English pound (very close to 460 grams). The Spanish libra equals 16 onzas, and the Portuguese libra equals 16 onças. The word "libra" is sometimes used now for the kilogram, a much larger unit.

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.