Quick answer: A fax number looks exactly like a phone number — a country code, an area code, then a local number. A US fax number is ten digits, written as (212) 555-0143 or +1 212 555 0143; an international one adds a country code, like +44 20 7946 0018 for the UK. Get every digit and the country code right and the fax lands; miss one and it goes nowhere.
Because a fax number is simply a phone number used for faxing, it follows the same format rules — but one wrong digit or a missing country code means your document doesn’t arrive. Below are concrete examples for the US and other countries, the rules for writing a number correctly, and two tools that check and format a number for you instantly.
What a fax number looks like
In the US, a fax number is ten digits: a three-digit area code followed by a seven-digit local number. You’ll see it written a few different ways, but the digits never change:
- (415) 555-0143 — the everyday form, with the area code in brackets
- 415-555-0143 or 415 555 0143 — the same number, hyphens or spaces
- +1 415 555 0143 — the international form, with the US country code (+1) in front
For long distance within the US you may need a leading 1 (1-415-555-0143), exactly as you would on a phone call. If you’re trying to read your own number rather than write someone else’s, see how to find your fax number.
Fax number examples by country
The pattern is the same worldwide — country code, area or city code, then the local number — but length and grouping vary. These show the format for each country; the digits are placeholders, not live numbers.
| Country | Country code | Example format |
|---|---|---|
| United States | +1 | +1 (212) 555-0143 |
| Canada | +1 | +1 (416) 555-0143 |
| United Kingdom | +44 | +44 20 7946 0018 |
| South Africa | +27 | +27 21 555 0143 |
| Philippines | +63 | +63 2 8555 0143 |
| Germany | +49 | +49 30 5550 0143 |
| Japan | +81 | +81 3 5550 0143 |
| Australia | +61 | +61 2 5550 0143 |
| France | +33 | +33 1 55 50 01 43 |
| India | +91 | +91 22 5550 0143 |
The same number has two faces: the international format (with the + and country code, for faxing in from abroad) and the national format (dropping the country code, sometimes adding a trunk 0 before the area code, for faxing within the same country). Online fax services accept the international + form from anywhere, which is why it’s the safest one to save.
Have a US number and want to check it? Paste it into the validator below — it confirms the format, identifies the state, and gives you the clean version.
US fax number lookup
US fax number validator
Paste any US fax number in any format — the validator strips it, checks it, identifies the state, and gives you the clean formatted version.
Enter a US fax number above to validate and format it.
Area code assignments are based on the North American Numbering Plan (NANP). Some area codes cover multiple states or are overlays serving the same geographic region. A valid format does not guarantee the number is active – always confirm with the recipient before sending.
How to write a fax number correctly
A fax number is built from three parts, and for international faxes a fourth marker in front:
- The + sign — signals an international number. From a US line you can dial 011 instead of + as the exit code.
- Country code — needed only for international faxes: +1 for the US and Canada, +44 for the UK, +49 for Germany.
- Area or city code — points the fax at a region. In North America it’s always three digits.
- Local number — the specific line. In the US that’s seven digits, giving ten in total before the country code.
Length is the detail that trips people up. A US number is ten digits; UK numbers run to ten or eleven; some countries reach fifteen. Include every part, and if you’re faxing abroad, don’t drop the country code — that single omission is the most common reason an international fax fails. If you’re dialling from a machine rather than an app, our guide to dialling a fax number covers when you need a leading 1 or an exit code.
Sending overseas and not sure how to lay out the number? The formatter below builds it for you.
Fax number formatter
International fax number formatter
Enter a local fax number, choose the country you are dialing to, and get the correctly formatted international number.
Formatted number
Enter a fax number above to see the formatted result.
Leading zeros are automatically removed from local numbers – most countries require this for international dialing. The + format is recommended for online fax services as it works regardless of which country you are sending from. Always confirm the number with your recipient before sending.
Special types of fax number
Most fax numbers follow the standard pattern above, but a few are worth recognising. Toll-free numbers use the 800, 888, 877 or 866 prefixes, so anyone in the country can fax them at no charge — common for customer-service and claims lines. Vanity numbers spell a word on the keypad, like 1-800-FAX-DOCS, purely to be memorable; they dial like any other number.
Online and virtual fax numbers look identical to traditional ones — same country code, area code and local number — because they run on the same numbering system; the difference is that they live in the cloud rather than on a phone line. If you don’t have a number yet, here’s how to get a fax number online.
