A Brief Guide To UK Postcodes

The postcoding system was devised by the Royal Mail to enable efficient mail delivery to all UK addresses. Initially introduced in London in 1857 the system as we now know it became operational for most of the UK in the late seventies.

Today the Royal Mail deliver to some 29 million addresses (also known as "delivery points").

There are approximately 1.8 million unit postcodes in use and each postcode covers an average of about 15 properties, however in reality it can be anywhere between 1 and 100.

Organisations that receive large volumes of mail are allocated individual postcodes. These are known as "Large User" postcodes and include PO Box addresses.

Postcodes are not static. New properties are constantly being built, old ones demolished, and the Royal Mail sometimes has to re-code within existing areas to maintain or improve distribution efficiency. So postcodes are added, deleted, and in some cases changed on an ongoing basis.


Postcode Structure


The postcode system is hierarchical, the top level being postcode area - 1 or 2 alpha e.g. "GU" or "B". For a complete list of postcode areas click here.

The next level is postcode district e.g. "GU1" or "B22". This is also commonly known as the "outcode" and generally provides the primary bulk sorting office routing information for the Royal Mail.

Next comes the sector e.g. "GU16 7", and then finally the unit e.g. "GU16 7HZ". The combination of sector and unit (the "7HZ" bit) is often called the "incode" and is used by the delivery offices to get the mail on the right vehicle (or bicycle) for final delivery.

The latest quarterly release counts can be found in the right column.

Please note that whilst the "inward" part of the postcode is always 1 numeric character followed by 2 alpha the "outcode" can be several different formats and anywhere from 2 to 4 alphanumeric characters long.

To uniquely identify each property within each unit postcode and to facilitate fully automatic sorting of bulk bar-coded mail the Royal Mail use an additional code called the "Delivery Point Suffix" This code (one numeric + 1 alpha e.g. "9Z") is not divulged to the general public and only used in bulk bar-coded mail applications.

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