How do you measure a nail?

In the United States of America, Nails are traditionally measured by length in inches and a unit the "penny". This "penny" unit is very old (going back to when square nails were individually handmade by blacksmiths) and literally specified the price of a certain quantity of nails (I think it was 100 nails, but I'm not sure). Thus you bought that quantity of 3-penny nails for 3 pennies and the same quantity of 10-penny nails for 10 pennies. However inflation has raised prices so much it obviously no longer means that and the "penny" unit has become a measurement of the nail diameter, while nails are now bought by weight instead of quantity ("I'll take a pound of 4 inch 10-penny nails."). Elsewhere, nails are measured in grams.