Postcodes explained

Christmas is just three weeks away and many of you (ok, some of you) will be writing your cards, buying stamps and desperately searching for your address book. Obviously your cards need accurate addresses in order to reach their intended destination, but what about the series of numbers and letters at the bottom of an address? What exactly is in a postcode?

Why do I need to use a postcode?

Postcodes allow your item to be processed quickly and accurately by pinpointing exactly where it needs to go. A single postcode is not unique to one address; usually a small group of addresses will share one postcode and the specific property will be identified by a house name or number. Using a correct postcode will allow your mail to go through the Royal Mail’s automated sorting machines. Mail without a postcode will have to be sorted manually and this takes much longer.

So how do postcodes work?

A postcode is split into four sections, each of which narrows down the destination. I’ll use the Simunix postcode (YO10 5NP) to demonstrate what each section means.


The first one or two letters identify the postcode area, in this case the YORK area, and therefore the main Royal Mail sorting office that will process the mail.


This part is usually either one or two numbers but some London postcodes contain a number and letter. This is the postcode district and tells the sorting office which delivery office the mail should go to.


The third part tells the delivery office which local area the mail should go to. This section usually just contains one number.


The final part always contains two letters and identifies groups of up to 80 addresses. This unit code tells the delivery office which postal route will deliver the mail.

How do I correctly address an envelope then?

The least amount of information that should be included in an address includes:

House name/number

Street name


Postcode (in capitals)

You do not need to include a County name if all the above information is provided. Of course, you may also wish to include the recipient’s name and perhaps a company or organisation name.

If you’re not sure what the correct postcode is for an address, you can look it up here by entering the address information you do have.

The latest recommended posting dates for Christmas 2014 (UK Inland) are:

Thursday 18th December – 2nd Class

Saturday 20th December – 1st Class