Most of the postal code systems are numeric; only a few are alphanumeric (i.e., use both letters and digits). ... For example, while a two digit numeric code can represent 100 locations, a two character alphanumeric code using ten numbers and twenty letters can represent 900 locations.

How is ZIP code written?

The letters are written properly in capital letters. The word ZIP was chosen to suggest that the mail travels more efficiently, and more quickly, when senders use it. The basic ZIP code is made up of five numbers. An extended ZIP + 4 code includes the five digits of the ZIP code, a hyphen and then four more digits.

Is ZIP code 2 words?

Since our caller works for the U.S. government, and ZIP codes are a government thing, I checked the US Printing Office style guide first. It recommends "ZIP Code." Associated Press style is similar: “ZIP code”—two words with “ZIP” in all caps—but it uses a lowercase C, and I was surprised it would deviate.