Both postcodes and zip codes route mail, but they're built differently — which matters whenever you design address forms for international customers.
Side by side
| UK Postcode | US Zip Code | |
|---|---|---|
| Format | Alphanumeric (SW1A 1AA) | Numeric (90210 / 90210-1234) |
| Precision | Up to ~15 addresses | Whole delivery area / town |
| Length | 5–7 characters | 5 or 9 digits |
| Resolves to address? | Yes, via PAF lookup | Approximate area only |
Designing global address forms
Use a neutral "Postal code" label internationally, and add UK address verification so UK customers get instant, accurate lookup.
More on postcodes
See how UK postcodes work or return to the PAF guide hub.
Frequently asked questions
What is the difference between a postcode and a zip code?
A UK postcode is alphanumeric (e.g. SW1A 1AA) and pinpoints up to ~15 addresses, while a US zip code is numeric (e.g. 90210) and covers a much larger delivery area.
Is a zip code the same as a postcode?
They serve the same purpose — routing mail — but differ in format and precision. UK postcodes are far more granular than US zip codes.
What should I call the field on an international form?
Use a neutral label like 'Postal code' for international forms, or localise it to 'Postcode' for UK and 'ZIP code' for US audiences.
We'll beat any like-for-like UK address lookup price
Send us your current quote or invoice and we'll come back the same working day with a better price — plus free migration and integration support.
- Beat any like-for-like UK quote, monthly or annual
- Free migration + hands-on integration support
- No setup fees, no lock-in, cancel any time
Ready to get started?
Add Royal Mail PAF-verified UK address lookup to your site in minutes — start free, no card required.