By David Thompson · Published January 17, 2026 · Updated June 8, 2026 · 5 min read
Quick Answer: A fax number is a regular telephone number connected to a fax machine or online fax service instead of a voice phone. It uses the same format as a phone number, but its purpose is to send and receive documents — not voice calls.
You can get a virtual fax number instantly through mFax.to — no landline or hardware needed.
You're filling out a form — maybe at a doctor's office, a bank, or the IRS — and you see a field that says "Fax Number." What exactly is that, and do you actually need one?
A fax number is simply a telephone number assigned to receive fax transmissions. When someone sends a fax to that number, the fax machine (or online fax service) on the other end picks up the call, receives the document data as audio signals, and converts it into a readable page. (The word "fax" is short for "facsimile," so a "facsimile number" means the same thing as a fax number.)
If you've ever wondered how a fax actually works, the fax number is the address that makes the whole system possible — just like an email address routes emails to the right inbox.
How Is a Fax Number Different from a Phone Number?
A fax number and a phone number use the exact same format and run on the same telephone infrastructure. The only difference is what's connected on the other end.
| Phone Number | Fax Number | |
|---|---|---|
| Format | (212) 555-1234 | (212) 555-5678 |
| What answers | A person or voicemail | A fax machine or fax service |
| What it receives | Voice calls | Document transmissions |
| Can you call it? | Yes — you'll hear a person | Yes — you'll hear screeching beeps |
What Happens If You Call a Fax Number?
You will hear a series of high-pitched beeps and screeches — the fax handshake — not a person. No voice conversation is possible. To send a document, hang up and use a fax machine or send your fax online instead.
Same Wire, Different Language
Think of it this way: a fax number is a phone number that "speaks fax" instead of speaking voice. The wire is the same. The protocol is different.
What Does a Fax Number Look Like? (Format & Examples)
A fax number looks exactly like a regular phone number — there is no visual difference. In the United States it is 10 digits: a 3-digit area code plus a 7-digit local number, such as (212) 555-1234, following the North American Numbering Plan (NANP).
US fax number format:
(Area Code) Local Number
(212) 555-1234
International fax number format:
+[Country Code] [Area Code] [Local Number]
+44 20 7946 0958 ← United Kingdom
+61 2 9876 5432 ← Australia
+81 3 1234 5678 ← Japan
When dialing an international fax, you'll need the exit code (011 from the US) followed by the country code and local number. Check our complete guide to international faxing for country-specific dialing instructions.
Don't Forget the Country Code
International faxes fail more often because of incorrect dialing format than for any other reason. Always include the + or exit code and the country code before the number.
How Many Digits Is a Fax Number?
In the United States, a fax number has 10 digits — a 3-digit area code plus a 7-digit local number — following the North American Numbering Plan (NANP). International fax numbers vary by country and may be longer once you include the country code.
Physical vs. Virtual Fax Numbers
There are two ways to have a fax number today: the old way (physical) and the modern way (virtual).
Physical Fax Number
A traditional fax number is tied to a landline connected to a physical fax machine. It requires:
- A dedicated phone line ($20–$40/month from a phone company)
- A fax machine with ink, paper, and power
- A physical location — you can only receive faxes where the machine sits
This was the only option for decades, and some offices still use it. But it's expensive, location-locked, and increasingly unnecessary.
Virtual Fax Number
A virtual fax number is hosted by an online fax service — no phone line, no machine, no hardware at all. When someone faxes your virtual number, the service receives the transmission and delivers it to you as a PDF via email, app notification, or web dashboard.
| Feature | Physical | Virtual |
|---|---|---|
| Monthly cost | $20–$40 (line) + machine | From about $9/mo |
| Setup time | Days (phone company install) | Minutes |
| Location | Fixed to one office | Anywhere with internet |
| Receive multiple faxes | One at a time (line is busy) | Unlimited simultaneous |
| HIPAA-ready | Depends on setup | Built-in with mFax Business |
For most people and businesses today, a virtual fax number is the better option. You can learn more in our virtual fax number guide.
Do You Need a Fax Number?
Not everyone needs their own fax number. Here's when you do — and when you don't.
You need a fax number if:
- You receive faxes regularly (from clients, vendors, or government agencies)
- Your industry requires it — healthcare, legal, insurance, and real estate still rely on fax
- You want a professional appearance on business cards and letterheads
- You need to receive faxes online without visiting an office
You don't need a fax number if:
- You only send faxes occasionally — services like mFax let you send without a dedicated number
- You fax once or twice a year — a pay-as-you-go fax service is more cost-effective
The Bottom Line
If anyone might need to fax something to you, get a virtual fax number. If you only send faxes outward, you can skip it and just use the mFax app.
How to Get a Fax Number Today
Getting a virtual fax number takes about 2 minutes:
- Visit mFax.to or download the mFax app
- Choose your number — pick a local area code or a toll-free number
- Start receiving faxes — incoming faxes arrive as PDFs in the app or via email
No phone company, no technician visit, no hardware. You can fax from your iPhone or computer the same day.
For business teams, mFax Business gives you virtual fax numbers, HIPAA compliance, and a shared dashboard — starting at about $9/mo (billed annually). There are no rigid fixed tiers: you build your own plan with a live calculator, choosing the exact seats and pages you need and paying only for what you use.
Send Your First Fax
Now that you understand what a fax number is, you're ready to use one. Download the mFax app or visit mFax.to, upload your document, and send. No machine. No store. No waiting.