Dozen: twelve eggs or twelve hundredweight?

To a baker or grocer, a dozen is simply twelve: twelve eggs, twelve rolls, twelve apples. The word comes from Old French douzaine, and the number 12 has been a standard commercial grouping for centuries in English-speaking trade. It is so familiar that we hardly think of it as a measure at all, just a convenient round number.

In metallurgy and ore trading, however, a dozen carries a specific weight: twelve hundredweight. A hundredweight is 112 pounds in the avoirdupois system used in Britain and its former colonies, so a metallurgical dozen equals 1,344 pounds of ore or metal. This definition appears in historical records of English mining and smelting, where ore was bought and sold by the dozen as a standard lot size. The measure persisted longest in trades dealing with heavy bulk materials, where consistency and established units of account mattered.

The divergence is neither linguistic nor conceptual but practical. In general commerce, twelve became the standard because it divides neatly into larger counts and fits human scale. In metallurgy, the dozen inherited from older English weights because ore comes in large quantities and dealers needed precision for high-value transactions. Once a definition became law or custom, miners and smelters used it for contracts and accounting, and the term stayed in use even as scientific measurement systems replaced it.

The metallurgical dozen is now obsolete in commercial practice, replaced by metric tonnes and pounds by weight. But it survives in historical documents, old contracts, and technical references as a ghost of how trade language can ossify around a single number. A dozen eggs will always be twelve; a dozen of ore, by the old measure, will always be 1,344 pounds.