* Postal Index Number or PIN or Pincode is the numbering of the post office or post code system used by India Post. The PIN code is 6 digits long.
* The first three digits of the PIN represent a specific geographical region called a sorting district that is headquartered at the main post office of the largest city and is known as the sorting office. A state may have one or more sorting districts depending on the volumes of mail handled.
* The fourth digit represents the route on which a Delivery office is located in the sorting district. This is 0 for offices in the core area of the sorting district.
* The last two digits represent the delivery office within the sorting district starting from 01 which would be the GPO or HO. The numbering of the delivery office is done chronologically with higher numbers assigned to newer delivery offices. If the volume of mails handled at a delivery office is too large, a new delivery office is created and the next available PIN is assigned. Thus two delivery offices situated next to each other will only have the first four digits in common.