CODEWITHSUNDEEP
regex
Zaphod Beeblebrox
Zaphod Beeblebrox

Reputation: 562

regex for UK postcode

I'm using the following javascript to check if a UK postcode is valid

var postcodeRegEx = /[A-Z]{1,2}[0-9]{1,2} ?[0-9][A-Z]{2}/i; 
if(postcodeRegEx.test($("#postcode").val())) { ... }

This works fine for mostly every postcode I've fired at it but for some reason WC2F 3BT doesn't return true.

Can anyone who understands regexbetter explain what the problem is and how I can fix it?

Upvotes: 0

Views: 6405

Answers (6)

Paul Taylor
Paul Taylor

Reputation: 5761

This one is comprehensive, covering London central postcodes as well as the standard X[X]n[n] nXX postcodes. (From Expresso Regex tool library).

\b([A-Z]{1,2}\d[A-Z]|[A-Z]{1,2}\d{1,2})\ +\d[A-Z-[CIKMOV]]{2}\b

Upvotes: 0

essiele
essiele

Reputation: 1

Remember, though, that some UK postcodes have only one letter in the first part (e.g. N1 7TE). So [A-Z]{2} would need to be [A-Z]{1,2}.

Upvotes: 0

user3639768
user3639768

Reputation: 121

/[A-Z]{2}\d[A-Z]?\s?\d[A-Z]{2}/i

This should match:

WC1E 7BT
CW3 9SS
SE5 0EG
SE50EG
se5 0eg

Upvotes: 0

Albzi
Albzi

Reputation: 15619

According to HTML5Pattern.com, a UK post code is:

[A-Za-z]{1,2}[0-9Rr][0-9A-Za-z]? [0-9][ABD-HJLNP-UW-Zabd-hjlnp-uw-z]{2}

Upvotes: 2

RobV
RobV

Reputation: 28675

If you want to understand what a specific regular expression is looking for there are lots of helpful online tools that will do this for you, my personal preference is http://regex101.com

The specific problem with your regular expression is that it assumes all postcodes are composed of one/two letters followed by one/two numbers and then a single number followed by two letters.

However this is not the case, as detailed in the wikipedia articles for UK Postcodes:

The 'outward' part identifies first the postcode area, using one or two letters (for example L for Liverpool, RH Redhill and EH Edinburgh). A postal area may cover a wide area, for example RH covers north Sussex, which has little to do with Redhill historically apart from the railway links, and Belfast (BT) covers the whole of Northern Ireland. These letter(s) are followed by one or two digits (and sometimes a final letter) to identify the appropriate postcode district (for example W1A, RH1, RH10 or SE1P)

Where the 'outward' part means the first half of the post code.

Therefore in order to cover all valid UK post codes you need to add an optional letter component as already detailed in other answers you've received, reproducing @Martyn's suggestion for completeness of this answer:

/[A-Z]{1,2}[0-9]{1,2}[A-Z]?\s?[0-9][A-Z]{2}/i

Upvotes: 1

Martyn
Martyn

Reputation: 806

/[A-Z]{1,2}[0-9]{1,2}[A-Z]?\s?[0-9][A-Z]{2}/i

You missed an optional letter, thats why it diddnt work. Your original regex was looking for one to two letters. Followed by two numbers possibly separated by a space.

Upvotes: 1

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