The Zip Code API provides the following functions for US zip codes:
Distance Between Zip Code API - The API allows you to quickly and easily figure out the distance between zip codes.
Zip Codes in Radius API - You can use this API to find all zip codes within a given radius from another zip code.
Zip Code to City and State API and Zip Code to Latitude/Longitude API - The API can convert a zip code to the primary location for the zip code. This includes the city, state, latitude, and longitude for the primary location.
City to Zip Code - This API looks up the Zip Code based on the City and State.