The short version
A post code is not a global standard. It is an internal routing code that each postal operator designed for sorting and delivery, not an administrative boundary. The US uses five digits. The UK mixes letters and digits. Japan always uses seven digits. Germany uses five. Canada needs only the first three characters to identify a delivery area.
The only reliable way to fill a form is: choose the country first, then follow that country’s format. Do not apply one country’s rules to another.
The five systems at a glance
| Country | Shape | Example | Granularity |
|---|---|---|---|
| United States | 5 digits, optional +4 | 90210 / 90210-1234 | City or delivery area |
| United Kingdom | 5–7 alphanumeric | SW1A / SW1A 1AA | District / address |
| Japan | 7 digits | 100-0001 | Town block |
| Germany | 5 digits | 01945 | One or more municipalities |
| Canada | 6 alphanumeric | M5V 1A1 | Area / address |
US ZIP: five digits for a delivery area
The first digit groups states, the next two identify a sectional center facility, and the last two identify a delivery area. 90210 is Beverly Hills, California. Adding four digits (ZIP+4) narrows it to a block or an organisation. Most checkout forms accept five digits; 90210-1234 is optional precision.
UK postcode: a delivery route in letters
A UK postcode has two parts: the outcode (SW1A) and the incode (1AA). SW1A 1AA is the full code around Buckingham Palace.
Many public datasets stop at the outcode because full Royal Mail address data is licensed. PostcodeDog now includes full GB post codes such as SW1A 1AA from OS Code-Point Open (Open Government Licence); Northern Ireland is still outcode-only. Street addresses are not included.
Japan: seven digits down to the town block
Japanese post codes are seven digits, written 100-0001. The first three digits identify the municipality; the last four identify the town block. 100-0001 is Chiyoda, Tokyo.
Japanese addresses run from large to small (prefecture → city → town → block), the opposite of most Western forms. Seven digits are enough; the hyphen is usually optional.
Germany: one code can cover several towns
German post codes are five digits. 01945 maps to nine places in Brandenburg in our data: Tettau, Guteborn, Grünewald, Hermsdorf, Lindenau, Ruhland, Kroppen, Hohenbocka and Schwarzbach.
This is not a data error. One delivery area can cover several neighbouring municipalities. When you see multiple places for a German code, check the state first and confirm with the recipient.
Canada: the first three characters are often enough
A full Canadian post code has six characters (the A1A 1A1 shape). The first three are the Forward Sortation Area (FSA); the last three are the Local Delivery Unit. M5V is downtown Toronto.
Public data usually stops at the FSA, so M5V still gets most deliveries done.
Why they were never unified
- Different histories: the US introduced ZIP in 1963; UK coding grew out of 19th-century postal districts.
- Different density: a rural delivery area may cover several towns, while an urban code may cover a few streets.
- Different licensing: full UK codes and Canadian LDUs are commercial datasets.
- Different carrier networks: last-mile sorting follows local operations, not administrative borders.
Three rules for filling the form
- Choose the country first. The field label and validation rules change with it.
- Keep leading zeros.
01945is not1945;00118is not118. - Do not invent precision. If you only have five digits, submit five; if you only have an outcode, submit the outcode.
FAQ
Can a post code identify a single address? No. It identifies a delivery area, which may contain many addresses, several municipalities, and sometimes codes shared across countries.
Why are some countries missing full codes? Most public datasets are limited by licensing to a district or FSA level. Full codes usually come from the national operator or a commercial address provider.
What happens if I get it wrong? At best the form rejects it; at worst the parcel is routed to the wrong sorting centre. For cross-border shipments, check country, state or province, city and post code together.