The postcode is made up of five to seven letters and numbers that indicate four different levels of a geographic unit. It’s part of a coding system developed by the Royal Mail and used to sort mail across the United Kingdom. Postcodes are an abbreviated form of address, that groups together delivery points (property or post boxes).

Full valid postcodes can be validated with AFD’s address lookup solutions at https://www.afd.co.uk/try-it/

There are two elements to each postcode. The outward postcode, or outcode, is the first portion. This is separated from the second part, which is the inward postcode, or incode, by a single space.

The outward postcode allows mail to be delivered to the right local area. Both area and district are contained within this part of the code.

The inward code sorts mail at each local area delivery office. Containing a numeric character that identifies the sector in the postal district then two alphabetic characters defining one or more properties within the sector.

For example: HD3 3WZ

HD states the postcode area of Huddersfield. The UK has 124 postcode areas in total.

HD3 is the postcode district in the postcode area of Huddersfield. There are 2,979 postcode districts.

HD3 3 refers to the postcode sector. There are 11,228 postcode sectors.

HD3 3WZ. The WZ completes the postcode. The last two letters define the ‘unit

postcode’ which identifies one or more small user delivery points – in the case of HD3 3WZ, 26 delivery points.

As of January 2022, there are  1,785,571 postcodes in the UK.