09/23/2026
In the United States nails are measured in “pennies,” so that a one-inch nail, for example, is called a “two-penny” nail (confusingly abbreviated as 2d nail—more on that below) and a two-inch nail is called a “six-penny” (6d) nail. Many thousands of you readers have probably long wondered how that came to be. Well, wonder no more.
The designation of nail sizes by “penny” originated in England in the Middle Ages, when, for example, 100 two-inch nails sold for six pennies, and thus came to be called “six-penny nails.” The size became so identified with the original price that even as the prices of nails changed, they were still called by the price they once had. (Just to keep things complicated, when designating quantities of nails in the Middle Ages, “one hundred” meant “long hundred” or “great hundred,” i.e. 120 nails, not 100.)
In the U.K. the “penny” measurement of nail sizes was phased out in the early 20th century. In the U.S., however, it has stubbornly persisted.
So why did the “penny” designation last so long? Economic historian Gregory Clark explains in this book A Farewell to Alms that it was because the price of nails changed so little over the centuries: “The near constancy of nail prices in nominal terms explains why in the United States nails are still designated as two penny nails or three penny nails. These were the prices of a hundred such nails in the fourteenth century in England. The terms became established as the names of particular types of nails since their prices changed so slowly.”
So what about the “d”? (In common usage, “6d” in reference to a nail size would be pronounced “six penny.”) That originated with the Latin word “denarius,” for the Roman coin most equivalent to a British penny, and abbreviated d. So, the English “penny” (or its plural, “pence”) came to be abbreviated “d,” and thus “6-penny” would be written “6d.”
Nowadays nails are more commonly sold by the pound. A one-pound box of common 6-penny (2-inch) nails (about 150 nails) costs about $6.
The image, from the 14th century Holkman Bible Picture Book, depicts a blacksmith forging a nail.
