Royal Mail UK Postcodes Explained

The Royal Mail maintains a master database containing every known deliverable address in the UK. On the file there are over 29 million deliverable addresses (including business addresses). These single household / business addresses share 1.756 million Postcodes.

The Postcode is part of a coding system created by the Royal Mail. The Postcodes are an abbreviated form of address, and enable a set of Delivery Points (normally letter boxes for addresses) to be grouped.

When originally created, the Postcode was ‘designed’ around the capability of Royal Mails' sorting equipment to read and interpret typed or handwritten text on mail. This is why Royal Mail prefers the Postcode to be separate and on the last line of an address.

The format and rules concerning Postcode layout, in particular which letters can or cannot be used, stem from the fact that certain characters or combinations of characters could be confused (e.g. ‘O’ with ‘Q’, or ‘V' 'V' with ‘W’).

A Postcode is a combination of letters and numbers which defines four different levels of a geographic unit. Each Postcode consists of two parts, called the Outward Code (e.g. ‘PO1’ 1AF) and the Inward Code (e.g. PO1 ‘1AF’). The first part, or Outward Code, is separated from the second part, the Inward Code, by a single space.

The Outward Code

Enables mail to be sorted to the correct local area for delivery. This part of the code contains the area and the district to which the mail is to be delivered, e.g. ‘PO1’, ‘SW1A’ or ‘B23’. The letters Q, V and X are not used in the first alpha position. The letters I, J and Z are not used in the second alpha position. The only letters to appear in the third position are A, B, C, D, E, F, G, H, J, K, P, S, T, U and W.

Inward Code

The second part is known as the Inward Code because it is used to sort the mail INTO the local area delivery office. This part is one number followed by two letters. The number identifies the sector in the postal district. The letters then define one or more properties in that sector. The letters C I K M O V are not used in the second part of the Postcode. In total, the Postcode is made up of 124 Areas, 2,827 Districts and 9,487 Sectors. These figures change frequently as address density and populations increase forcing the Royal Mail to split an area (and its postcode) assigning new postcodes.

Postcodes Explained - Page 2 of 2

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