Carmarthenshire Postcode Statistics

Carmarthenshire has 9,607 active postcodes spread across 20 postcode districts. This figure comes from the National Statistics Postcode Lookup published by the Office for National Statistics, which is updated four times a year in February, May, August and November. The count rises gradually as new housing estates and commercial premises are completed and assigned codes, and falls occasionally when buildings are demolished and their codes formally retired. Each active postcode in Carmarthenshire identifies a distinct delivery point, from a large office building with its own dedicated code to a street of houses sharing a single postward assignment.

The largest district by postcode count is SA4, covering Swansea.

Carmarthenshire is served by 20 postcode districts, each identified by an outward code: the letters and number that appear before the space in a full postcode. The outward code directs mail to the relevant sorting office and delivery area; the inward code after the space then narrows delivery to a specific street or group of properties. District sizes across Carmarthenshire vary considerably. Urban districts in the county's larger towns and cities can each cover thousands of closely packed addresses, while rural districts often serve scattered settlements spread across a much wider geographic area. The table above ranks every Carmarthenshire district by active postcode count.

See all Carmarthenshire districts on the Carmarthenshire postcodes page.

SA4, which serves Swansea, is the Carmarthenshire district with the greatest number of active postcodes at 1,132. A high postcode count within a district generally reflects address density rather than geographic size: compact urban neighbourhoods generate far more postcodes than sprawling countryside districts simply because the number of individual delivery points is greater. You can browse every active postcode within SA4, along with street names and location details, on the SA4 district page.

The postcode districts assigned to Carmarthenshire cover a total population of 277,888 people across an estimated 114,656 households, based on ONS mid-year population estimates and the 2021 census. These figures are allocated to postcode districts using address-weighted methods and represent the residential population of the covered area rather than an exact head count. Business premises, industrial sites and non-residential addresses contribute to the postcode count but are excluded from the population and household totals. Density varies significantly across Carmarthenshire: postcodes in the county's built-up centres serve far more residents per code than those covering agricultural land or sparsely populated rural settlements.

Every individual unit postcode in Carmarthenshire is assigned to exactly one local authority in the ONS dataset. However, postcode districts frequently straddle council boundaries, which means that looking up a district code alone will not always identify which council is responsible for a specific address. Two neighbouring properties can sometimes belong to different councils even when they share a postcode district. For questions about council tax, planning permission, waste collection or school catchment areas, always verify the full unit postcode using the search tool at the top of this page rather than assuming the district assignment is definitive.

Postcode area boundaries were drawn by Royal Mail to reflect sorting and delivery logistics, not county lines or local authority borders. As a result, some addresses near the edges of Carmarthenshire fall within a postcode area whose letter code is historically associated with a neighbouring county or city. This happens wherever the nearest Royal Mail sorting office lies just across what is now a county boundary. It is not an error: the postcode area code simply identifies which facility processes the mail, and the ONS dataset correctly assigns each such postcode to its actual local authority regardless of which area letters it carries.

The ONS publishes a revised postcode dataset every quarter. Each release can add new codes for newly completed housing estates, commercial premises and mixed-use developments, amend records where delivery arrangements have changed and formally terminate codes that are no longer in use. Nationally, around 3,000 postcodes change status per quarter; Carmarthenshire will typically see a smaller proportion of that total, concentrated in areas of active construction or regeneration. Population and household figures for Carmarthenshire districts are updated less frequently, following each new ONS annual population estimate or census release.

Type any full postcode into the search bar at the top of this page. The result will show the exact delivery location, the local authority and ward it falls within, the parliamentary constituency, the ONS region, coordinates and a list of nearby postcodes ordered by distance. If you know the district but not the full code, use the links in the district table above to browse every active postcode within that area of Carmarthenshire. The Carmarthenshire postcode directory lists all 20 districts with individual links, making it straightforward to work from a neighbourhood or town down to a specific code.

You can also compare Carmarthenshire with other counties on the UK postcode statistics page.