Countries
United Kingdom Postal Codes and Addressing Guide
How UK postcodes and addresses work, how to write them, and how a UPCS GB code can sit alongside a normal UK address as an exact-location add-on.
Updated 14 October 2026 · 3 min read
The United Kingdom uses an alphanumeric postcode system run by Royal Mail. A postcode is a short mix of letters and digits that narrows an address down to a street or a small group of properties, which is far more precise than the postal codes of many other countries.
How UK postcodes work
A postcode has two halves separated by a space. The first half, the outward code, identifies the postcode area and district used for sorting mail. The second half, the inward code, narrows delivery down to a sector and a unit, which is often one side of a street or a handful of buildings. Letters and digits are always combined, so a UK postcode looks quite different from the all-numeric codes used in many other countries.
Because a postcode is so fine-grained, a UK address is often unambiguous with only a house number or name plus the postcode. The full rules are in UK postcode format explained.
How addresses are written
British addresses run from the most specific detail to the most general: the recipient, the building or flat, the house number and street, the town, and finally the postcode on its own line. A county is not required for the postal system to route an item. Details and an example are in how to write a UK address correctly.
How UPCS codes work in the United Kingdom
UPCS generates a short code for an exact spot chosen on a map. In the United Kingdom the code begins with the prefix GB, followed by two blocks of letters and digits, for example GB-XXXX-XXXX (a placeholder, not a real code). Each code stands for a 3 m x 3 m grid cell, and the same coordinates always give the same code.
A UPCS code is not an official postcode. It is not issued by Royal Mail or any government body and does not replace the postcode on a parcel. It is a complement: it lets a delivery driver, visitor or shop open the precise entrance, gate or pick-up point on a map.
In this guide
This guide has four more pages. Postcode format explains the structure of the code itself. Address format covers line order and conventions. Finding a postcode shows how to look one up and check it. Delivery and addressing challenges looks at what makes some UK deliveries difficult and how an exact-location code helps. For other countries, see the countries hub.
In this guide
Frequently asked questions
Is a UPCS code the same as a UK postcode?
No. A UK postcode is assigned by the postal operator and is used for mail sorting. A UPCS code is a separate code for an exact 3 m x 3 m location and is not issued by any postal operator.
Does the UK use a prefix for UPCS codes?
Yes. UPCS codes for locations in the United Kingdom start with GB, for example GB-XXXX-XXXX in the standard CC-XXXX-XXXX layout.