Postcode Lookup Explained

A postcode lookup is a tool that connects addresses and postcodes. Depending on the tool, you give it one and get the other. The accuracy depends entirely on the data behind it.

The main types

• Address to postcode: you enter a street and number, and it returns the code. This is what most people need; see how to find a postcode.
• Postcode to addresses: you enter a code and get a list of addresses that use it, so you can pick yours. This speeds up checkout forms.
• Postcode to area: you enter a code and get the town, region or approximate map point; see can a postcode be converted to coordinates.

Where the data comes from

The most authoritative data comes from the national postal operator. Other providers license or derive data from it and repackage it. Because of that, the freshness of results depends on how often the provider updates; see how postcode systems are maintained.

Where lookups help

• reducing typing on mobile devices
• cutting down the chance of errors, such as those in common postcode mistakes
• filling in town and region automatically
• giving instant delivery availability

Where they fall short

A lookup can only return what exists in its data. New buildings, informal addresses and recently changed codes may be missing. In countries without a postcode system there is nothing to look up. A list may also show addresses with a postcode but not their exact location on the ground.

Postcode lookup versus code lookup

Do not confuse a postcode lookup with a lookup of an exact-location code. On UPCS, pasting a code such as PK-1A2B-3C4D into the search box shows the country, coordinates and map options for that 3 m by 3 m cell. It does not return postal addresses and UPCS does not offer address autocomplete or address validation. Developers can read the API documentation for the code lookup endpoint.

Key takeaway

Before relying on any lookup, test it with a few addresses you know, including a recent development and a rural property. The results will show quickly how fresh and complete its data is, and whether you need a manual fallback for the addresses it cannot find.