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There are times when you may want to use the 9 digit zip code validation for US. The 9 digit zip code is usually in format like this #####-####. For a 9 digit US zip code validation use below regular Expression. ^([0-9]{5}-[0-9]{4})$.
The basic format consists of five decimal numerical digits. An extended ZIP+4 code, introduced in 1983, includes the five digits of the ZIP code, a hyphen, and four additional digits that determine a more specific location within a given ZIP code. The USPS provides a free online lookup tool for ZIP codes.