How Do Postcodes Work?

A UK postcode is made up of two alphanumeric codes that show an 'Outward Code' (the first part) and an 'Inward Code' (the second part). An 'Outward Code' has anywhere from 2 to 4 characters but the 'Inward Code' always has only 3.

An 'Outward Code' indicates a postcodes area and distrct and the 'Inward Code' indicates a postcode sector and unit.

Outward Inward
Area District Sector Unit
1 or 2
1 or 2 digits
1 digit & 1 character
1 digit 2 characters
Wimbledon - SW19 5AE
SW 19 5 AE
Liverpool University - L1 8JX
L 1 8 JX
10 Downing Street - SW1A 2AA
SW 1A 2 AA

Outward Code (Outcode)


The postcode area can be 1 or 2 characters long and is always made up of alphabetical characters. The area can cover a large region of the country.


A postcode district can be 1 or 2 digits OR 1 digit followed by 1 letter.

Inward Code (Incode)


A postcode sector is made up of a single digit.


A postcode unit is two alphabetical characters and represents a street, part of a street, group of properties, or a single address or destination. It is the smallest unit of the postcode and the size of what it represents is normally determined by the amount of post recieved at the destination. For example PR8 9PW is the postcode of the UK Passport Office and covers more than one physical address as it receives a large amount of mail.

How Many Postcodes Are There In the UK?

As of February 2022 there were 1,785,448 active postcodes in the UK, Northern Ireland, Channel Islands and Isle of Man.

Active UK Postcodes
As of February 2022