Do I need to dial "9" before a fax number?

Only in office buildings with a PBX phone system. At home or when using an online fax service like mFax, you never need to dial 9. The "9" tells a corporate phone system to route your call outside the internal network.

Do I need to dial "1" before a fax number?

Yes, for long-distance calls within the US and Canada. The "1" is the North American country code and is required when dialing across area codes for most physical fax machines. Online fax services like mFax handle this automatically — just enter the 10-digit number.

How do I dial an international fax number?

From the US using a physical machine, dial 011 + country code + local number. Using an online fax service, use the + format: +44 20 7946 0958. See our [complete guide to international faxing](/blog/complete-guide-international-faxing/) for country codes and rates.

Why is my fax not going through after I dial the number?

The most common causes are a missing prefix (forgot "1" for long distance), a wrong country code for international faxes, or — on an office machine — forgetting to dial "9" first. Online fax services eliminate all of these issues by handling prefixes for you.

What is the difference between a fax number and a phone number?

A fax number and phone number use the same format — 10 digits in the US. The difference is what's on the other end: a fax machine answers with a tone, not a voice. Learn more in our guide to [what is a fax number](/blog/what-is-a-fax-number/).

How to Dial a Fax Number (Local, Long Distance & International)

Dialing a fax number wrong is the #1 reason faxes fail. This guide explains exactly when to use "1", "9", "011", or "+" so your document goes through on the first try — whether you're faxing locally, long distance, or overseas.

Frequently Asked Questions

Do I need to dial "9" before a fax number?: Only in office buildings with a PBX phone system. At home or when using an online fax service like mFax, you never need to dial 9. The "9" tells a corporate phone system to route your call outside the internal network.
Do I need to dial "1" before a fax number?: Yes, for long-distance calls within the US and Canada. The "1" is the North American country code and is required when dialing across area codes for most physical fax machines. Online fax services like mFax handle this automatically — just enter the 10-digit number.
How do I dial an international fax number?: From the US using a physical machine, dial 011 + country code + local number. Using an online fax service, use the + format: +44 20 7946 0958. See our [complete guide to international faxing](/blog/complete-guide-international-faxing/) for country codes and rates.
Why is my fax not going through after I dial the number?: The most common causes are a missing prefix (forgot "1" for long distance), a wrong country code for international faxes, or — on an office machine — forgetting to dial "9" first. Online fax services eliminate all of these issues by handling prefixes for you.
What is the difference between a fax number and a phone number?: A fax number and phone number use the same format — 10 digits in the US. The difference is what's on the other end: a fax machine answers with a tone, not a voice. Learn more in our guide to [what is a fax number](/blog/what-is-a-fax-number/).