USPS Postal Zones are how the United States Postal Service determines the distance between an origin and destination address. These zones range from 1-9, where Zone 1 is a local shipment and Zone 9 is the furthest possible distance for a domestic shipment.
At this time, ShipStation only supports displaying zones as defined by USPS. We are not able to display zone information from other carriers. Even though zones are USPS-specific, the information can be helpful when using other carriers, since they are representative of the distance between the ship from and destination address.
To view the zone relationship between a postal code and all others based on their first three digits, use the USPS Domestic Zone chart.