UK Postcode Format

Everything developers need to know about UK postcode structure, validation, and working with postcode data in applications.

What is a UK Postcode?

A UK postcode is a series of letters and numbers that identifies a specific geographic area for mail delivery. Every UK address has a postcode. There are approximately 1.7 million active UK postcodes covering England, Scotland, Wales, and Northern Ireland.

UK postcodes are not the same as ZIP codes used in the USA. They are more granular — a UK postcode typically covers around 15 properties on a single street.

UK Postcode Structure

A UK postcode has two parts separated by a space:

The outward code itself has two parts:

UK Postcode Examples

Valid UK Postcode Formats

There are several valid postcode formats depending on the area code length and district format:

UK Postcode Validation Regex

Use this regex to validate UK postcodes in your application. It handles all valid UK postcode formats including special cases:

// JavaScript
const UK_POSTCODE_REGEX = /^[A-Z]{1,2}[0-9][0-9A-Z]?\s?[0-9][A-Z]{2}$/i;

// Usage
UK_POSTCODE_REGEX.test('NR21 8AB');  // true
UK_POSTCODE_REGEX.test('NR218AB');   // true (no space accepted)
UK_POSTCODE_REGEX.test('ZZ99 9ZZ');  // false (invalid)

# Python
import re
UK_POSTCODE_REGEX = re.compile(r'^[A-Z]{1,2}[0-9][0-9A-Z]?\s?[0-9][A-Z]{2}$', re.IGNORECASE)

UK_POSTCODE_REGEX.match('NR21 8AB')  # Match
UK_POSTCODE_REGEX.match('SW1A 1AA')  # Match

# PHP
$pattern = '/^[A-Z]{1,2}[0-9][0-9A-Z]?\s?[0-9][A-Z]{2}$/i';
preg_match($pattern, 'NR21 8AB');  // 1 (match)

Normalising UK Postcodes

Before validating or looking up a postcode, normalise it to a consistent format:

// JavaScript — normalise to uppercase with space
function normalisePostcode(raw) {
  const p = raw.toUpperCase().replace(/\s+/g, '').trim();
  return p.slice(0, -3) + ' ' + p.slice(-3);
}

normalisePostcode('nr218ab');   // 'NR21 8AB'
normalisePostcode('SW1A1AA');   // 'SW1A 1AA'
normalisePostcode(' ec1a 1bb '); // 'EC1A 1BB'

Getting Postcode Data via API

Once you have a valid, normalised UK postcode, you can look up coordinates, drive times, and street names using the Job Bookers Routing API.

GET https://api.jobbookers.co.uk/v1/geocode?postcode=NR21+8AB

{
  "postcode": "NR21 8AB",
  "lat": 52.83162,
  "lon": 0.87049
}