UK Postcode Checker & Reference
Check whether a UK postcode is in the right format and in use, see what each part means and which area and town it belongs to, and look up its council and constituency if you need to.
About this tool
A UK postcode has two halves. The outward code (SW1A) gets mail to the right delivery office: SW is the postcode area and SW1A the district. The inward code (1AA) is used for the final sort: 1 narrows it to a sector and AA to a unit, typically a street or part of one with 15 to 20 addresses, or a single large organisation. The tool checks Royal Mail’s rules, such as which letters can appear where, and explains anything wrong.
It then looks the postcode up in the ONS Postcode Directory built into the page, to confirm the district and sector are in use and to give an approximate location and the main town. That happens in your browser. Only the online button sends the postcode anywhere: it asks postcodes.io for the exact location, council, ward and parliamentary constituency, and whether an old postcode has been taken out of use. Guernsey, Jersey and the Isle of Man have their own postcodes but aren’t in the UK data. Your last postcode is remembered on this device.
Contains OS data © Crown copyright and database right 2026. Contains Royal Mail data © Royal Mail copyright and database right 2026. Source: Office for National Statistics, Open Government Licence v3.0.