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Home > Guides > ZIP code vs postal code
A ZIP code is the American system: five digits, sometimes followed by four more, all numbers. A postal code is the Canadian system: six characters alternating letter and number, with a space in the middle. The two are not interchangeable, and putting one country's format on the other's mail slows sorting or sends the letter back. Use the format of the destination country.
ZIP stands for Zone Improvement Plan, a name USPS introduced in 1963 to speed up sorting. The five digits work from broad to narrow: the first digit names a region of the country, the next two point to a sectional center, and the last two narrow it to a post office or delivery area. A familiar example is 90210 for Beverly Hills, California. The optional ZIP+4 adds a hyphen and four more digits that narrow the destination to a block, a building, or a specific delivery point, which helps machines sort mail to the exact carrier route.
ZIP+4 is worth using when you know it, because it cuts down manual handling. A five-digit ZIP alone still works, but the extra four digits let the sorting machine place the letter closer to its final route on the first pass. You can find a ZIP+4 through the USPS lookup tool or from mail the recipient has already sent you, since return addresses on business mail often carry the full code.
Canadian postal codes use six characters in a letter-number-letter, space, number-letter-number pattern, such as K1A 0B1 for Canada Post's headquarters in Ottawa. The first three characters, called the forward sortation area, name a region and a major sorting district. The first letter alone names a province or territory, which is why codes starting with M sit in the Toronto area and codes starting with V sit in British Columbia. The last three characters, the local delivery unit, narrow the destination to a street block, a building, or a rural route.
Two details trip people up. First, the space in the middle is part of the format, and while machines usually cope without it, the spaced form is the correct one. Second, Canadian postal codes skip certain letters: D, F, I, O, Q, and U never appear, because they look too much like other characters when scanned or hand-read. If you see one of those letters in a Canadian code someone gave you, it is almost certainly a transcription error.
| Feature | US ZIP code | Canadian postal code |
|---|---|---|
| Format | Five digits, optional ZIP+4 | Letter-number-letter, space, number-letter-number |
| Example | 90210, or 90210-1234 | K1A 0B1 |
| First character means | A region of the US | A province or territory |
| Precision | ZIP+4 reaches a block or building | Last three characters reach a block or building |
| Letters used | None, digits only | All except D, F, I, O, Q, U |
Sorting machines read the code first and the street address second. A Canadian-style code on a US-bound letter confuses the machine, because it expects digits, and the letter drops into a manual pile or gets returned for a bad address. A five-digit number on a Canadian-bound letter is equally useless, because Canadian sorting expects the letter-number pattern and has no way to place a bare number. Even a correct code in the wrong position causes trouble: the code belongs on the same line as the city and state or province, at the end of the address, not on its own line or above the street address.
The most common real-world mix-up is Americans writing "ZIP code" on a form for a Canadian address, and Canadians writing "postal code" for an American one, then entering a code in the wrong format. Online forms sometimes compound the problem by validating strictly: a US form may reject a Canadian code outright, and a Canadian form may reject a five-digit entry. When a form fights you, check which country's address you are entering and switch the country field first, because that usually changes the validation rules.
Cross-border mail needs the destination country's format, plus the country name in capital letters on the last line. A letter from Toronto to Chicago carries a five-digit ZIP code and "USA" on the final line. A letter from Chicago to Toronto carries a Canadian postal code and "CANADA" on the final line. The country line matters because it tells the sending country's system to route the letter internationally instead of trying to match it to a domestic address.
With LetterAgent, you mail letters to US or Canadian recipients by asking your AI assistant, and the recipient's address shows through the window of a double-window envelope, so the code must be right in the address you provide. Double-check the code against the recipient's own mail or a postal lookup before approving the quoted price, since a wrong code is the simplest addressing error to make and one of the hardest to fix after the letter is printed.
Ready to mail it? Send your letter with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it is printed and mailed.
LetterAgent is a working name. Prices include print, postage, and our service fee. US prices in USD, Canadian prices in CAD (Canadian prices exclude applicable sales tax, added at checkout). Currently in private testing.
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