Why do mobile numbers have 10 digits?

Most countries use 10-digit mobile numbers because 10 digits give 10 billion (10^10) unique combinations, comfortably more than the world's roughly 8.6 billion mobile subscriptions, while staying short enough for people to remember and dial. Shorter numbers (e.g., 9 digits = 1 billion combinations) would not provide enough room for growth, reserved blocks, and special-purpose numbers.

Are all phone numbers in the world 10 digits?

No. While the US, Canada, Australia, and India use 10-digit numbers (excluding country codes), several countries use 11-digit numbers — China and the UK among them. The actual length is set by each country's national numbering plan.

What do the digits of a phone number represent?

In the US and Canada (North American Numbering Plan), a 10-digit number splits 3-3-4: a 3-digit area code (NPA), a 3-digit central office prefix (NXX), and a 4-digit line number. Other countries split the digits differently (India uses 2-3-5; UK landlines use 3+8, 4+7, or 5+6), but the digits always identify a country, a network or geographic region, and a specific line.

Why do Chinese phone numbers have 11 digits?

China's national numbering plan allocates 11 digits to mobile numbers (all starting with 1) to leave room for a population of over 1.4 billion plus multiple competing carriers (China Mobile, China Unicom, China Telecom) each requiring their own prefix ranges. Unlike Chinese landlines, mobile numbers do not require a leading 0 trunk prefix.

What does MSISDN stand for?

MSISDN stands for Mobile Station International Subscriber Directory Number. It is the full international phone number used to reach a mobile subscriber, defined by the ITU-T E.164 standard, and consists of a country code, a national destination code, and a subscriber number.

Why Mobile Numbers Have Exactly 10 Digits? Why Not Less Or More?

Table of Contents (click to expand)

Phone Numbers And Population Explosion
All About Numbers
What Do The Digits Of A Mobile Phone Number Represent?
The Need For Eleven Digits
Understanding Numbers

Most countries (including the United States, Canada, Australia, and India) use 10-digit mobile numbers because 10 digits give 10 billion (10¹⁰) unique combinations, comfortably more than the world's roughly 8.6 billion mobile subscriptions, while still being short enough for people to remember and dial. A few countries, such as China and the UK, use 11-digit numbers.

Imagine you have two cards and two envelopes—2 are blue, and two are yellow. Now, how many possible ways can you arrange them in a pair?

Blue card-Yellow card, Blue card-blue envelope, Blue envelope-yellow envelope, blue envelope-blue card; 4 ways.

This answer could also be predicted using ‘Permutations and Combinations,’ simply math combined with logic.

Simply put, the equation is this: 2 (no. of cards) x 2 (no. of envelopes) = 4.

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Phone Numbers And Population Explosion

It may not seem related, but the same principle can be applied to the number of digits in mobile phone numbers. This depends on the number of mobile phone users, as there should be more available mobile numbers than users.

mobile growth in india — Growth of mobile users in India. (Photo Credit: Public Domain Picture / Wikimedia Commons)

As of 2025, the GSMA estimated about 5.8 billion unique mobile subscribers worldwide (and roughly 8.6 billion active SIM-card connections, since many people carry more than one). With the global population still growing toward 9–10 billion by mid-century, any national numbering plan has to leave plenty of room: there must be far more available numbers than there are people who might ever need one.

All About Numbers

Returning to Permutations and Combinations, how many single-digit numbers do we know? 10.

Thus, if phone numbers were to have two digits, how many different number combinations would be available? 10 x 10 = 100.

Similarly, if phone numbers were only nine digits long, that would cap us at one billion subscribers (10⁹), which the world's mobile network already exceeds many times over.

Hence, the 10-digit mobile number. This offers 10 billion different combinations (10¹⁰), comfortably larger than the global population, with plenty of headroom for spare and reserved blocks that the regulator can't actually assign to subscribers.

What Do The Digits Of A Mobile Phone Number Represent?

What does a 10-digit phone number actually represent?

Well, it's not just a group of numbers strung out at random. The exact breakdown depends on the country, but the digits always carve up into a few meaningful chunks. In the United States and Canada (which share the +1 North American Numbering Plan), a 10-digit number splits 3-3-4: a 3-digit area code (NPA), a 3-digit central office prefix (NXX), and a 4-digit line number. For example:

(210) 745-7467

Area code (NPA) = 210 (San Antonio, Texas)

Central office prefix (NXX) = 745

Line number = 7467

India uses a different 2-3-5 split (a 2-digit access code, a 3-digit operator code, and a 5-digit subscriber code), and the UK uses 4-3-4 or 5-3-3 for landlines, with mobile numbers all starting with 07. The exact slicing differs, but the principle is the same: the digits route your call from a country, to a network, to a specific line.

The Need For Eleven Digits

Mobile Numbers Made In China

However, like all mundane things, there are exceptions to the 10-digit mobile number, and no, it’s not because of the country code.

China has 11-digit mobile numbers (excluding the country code +86). The country code +1, by the way, isn't just for the United States; it's the North American Numbering Plan, shared by the US, Canada, and most Caribbean nations. In China, all mobile numbers begin with the digit 1 (landlines do not), so two systems aren't actually in conflict.

Keyboard Mobile Phone Telefonia Numbers Keys — All mobile numbers in China start with 1. (Photo Credit: MaxPixel)

Let's take an example Chinese mobile number:

135 6435 467X

The first three digits identify the service provider. Looking at the 135 prefix, we can tell the carrier is China Mobile. Different leading triplets (such as 130–139, 150–159, 170–179, 180–189, 199) were allocated to different carriers (China Mobile, China Unicom, and China Telecom) over the years as China's mobile network grew. The 139 prefix was the first GSM range issued by China Mobile (in 1994), with 138 following in 1997, and the 137/136/135 ranges added later as demand exploded.

Unlike Chinese landlines, mobile numbers in China do not require a leading "0" trunk prefix or a city code; you dial the full 11-digit number directly, anywhere in mainland China. (The leading-0 + area-code rule only applies to landlines.)

Numbers From The UK

Most UK phone numbers are 11 digits when written domestically (starting with a leading "0" trunk prefix), which becomes 10 digits in international format after the +44 country code.

UK landlines use a geographic area code followed by a local subscriber number, with the two chunks splitting 3+8, 4+7, or 5+6 depending on the city's code length. For example, Leicester landlines use the area code 0116, so a Leicester landline might be dialed as 0116 986 6574.

UK mobile numbers are different: they don't use geographic area codes at all. Every mobile number starts with the prefix 07 (followed by 9 more digits), for example 07700 900123. In international form, drop the leading 0 and prepend +44, giving +44 7700 900123.

Understanding Numbers

Mobile numbers are sometimes referred to as the address of a person for a very good reason.

When speaking globally, the Mobile Station International Subscriber Directory Number (MSISDN) and the International Mobile Subscriber Identity (IMSI) identify mobile subscribers internationally.