dozen

In metallurgy and ore trading, a dozen is a unit of mass equal to 12 hundredweight. Since one hundredweight (cwt) equals 112 pounds, a dozen totals 1,344 pounds or roughly 610 kilograms. This measure originated in medieval England and persists in some metal trades, particularly in historical records, old contracts, and among dealers in salvage and recycled metals who still reference imperial weights.

The dozen appears most often in contexts where ore or metal is bought and sold by the lot rather than by individual ingots or processed sheets. A merchant purchasing tin ore, lead ore, or copper ore by the dozen could expect to receive material amounting to just over three-quarters of a metric ton. Because the unit bundles 12 hundredweights, it offers a convenient scale for cargo manifests and trade documentation, sitting between the hundredweight (small unit) and the ton (large unit).

The dozen in ore trading differs sharply from the common dozens (12 items) used elsewhere in manufacturing and commerce. A metalworker ordering a dozen ingots receives 12 pieces; a dealer ordering a dozen of ore receives 1,344 pounds of mixed material. This ambiguity has caused errors in modern supply chains, particularly when legacy specifications are not clearly labeled as weight-based rather than count-based.

Today the dozen appears rarely in new contracts or digital stock systems, which default to kilograms or metric tons. However, it survives in auction catalogs for scrap metal, in insurance valuations of estate collections, and in technical literature predating the 1970s adoption of metric weights in most English-speaking countries. Anyone working with historical mill records, old assay reports, or inherited trading agreements should recognize the dozen as a weight unit, not a quantity.