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RJ12 vs. RJ45: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on April 19, 2024
RJ12 and RJ45 are both types of connectors, with RJ12 typically used for telephone wiring and RJ45 predominantly used for network cabling.

Key Differences

RJ12 connectors are used primarily in telephone systems and are smaller in size. They typically have six positions and six connections (6P6C). RJ45 connectors are larger, used mainly for network cabling, and typically have eight positions and eight connections (8P8C).
The RJ12 connector is commonly found in residential telephone connections and some small office communication equipment. In contrast, RJ45 is the standard for Ethernet and network cables, used extensively in computer networking.
RJ12 and RJ45 connectors differ in their physical dimensions and cannot be used interchangeably. RJ45's larger size accommodates more wires, essential for network data transmission, while RJ12's smaller size suits the lesser requirements of telephone wiring.
RJ12 connectors are less common today due to the decline in traditional telephone systems, while RJ45 connectors are ubiquitous in modern digital and network infrastructures, reflecting the shift towards internet-based communication.
In terms of technical specifications, RJ12's bandwidth and data transmission capabilities are much lower than those of RJ45. RJ45 connectors support high-speed data transfer required for internet and Ethernet connections.

Comparison Chart


Primarily for telephone systems
Predominantly for network cabling

Connector Size

Smaller, 6P6C
Larger, 8P8C

Application Context

Residential phones, small offices
Computer networking, Ethernet

Physical Dimensions

Cannot be interchanged with RJ45
Larger than RJ12

Data Capabilities

Lower bandwidth and data transfer
High-speed data transmission

RJ12 and RJ45 Definitions


Less common in modern digital infrastructure.
As digital communication advances, RJ12 connectors are becoming less prevalent.


Essential in modern computer networking.
Our office network is set up using RJ45 cables for all connections.


A connector used in telephone systems.
The home telephone system uses an RJ12 connector.


Supports high-speed data transfer.
For optimal internet speeds, use an RJ45 cable for your router.


Known for its 6P6C configuration.
RJ12 connectors, with their 6P6C design, are standard in older telephone setups.


A connector primarily used for Ethernet networking.
To set up a wired internet connection, you'll need an RJ45 cable.


Used in some small office communication devices.
Our office's fax machine connects via an RJ12 port.


Larger and not interchangeable with RJ12.
Ensure you're using an RJ45 connector for your network, not an RJ12.


Smaller than RJ45 connectors.
For the telephone line, you'll need the smaller RJ12 connector, not the RJ45.


Characterized by its 8P8C configuration.
The RJ45's 8P8C structure makes it suitable for Ethernet connections.


What is an RJ12 connector?

RJ12 is a connector used mainly in telephone systems.

Can RJ12 be used for internet?

RJ12 is not typically used for internet connections.

What is an RJ45 connector?

RJ45 is a connector used for Ethernet and network cabling.

Are RJ12 connectors still used today?

RJ12 connectors are less common but still used in some telephone and small office systems.

Can RJ12 and RJ45 connectors be interchanged?

No, due to their different sizes and configurations, they cannot be interchanged.

Is RJ45 used for all network cabling?

RJ45 is the standard connector for most network and Ethernet cabling.

Why is RJ45 preferred for Ethernet?

RJ45 supports higher data transfer rates, essential for Ethernet networks.

What does 6P6C mean for RJ12?

6P6C means six positions and six connections, a standard for RJ12.

Do RJ12 connectors support high-speed internet?

RJ12 is not designed for high-speed internet; it's mainly for telephone frequencies.

Is RJ45 compatible with RJ12 ports?

RJ45 is not compatible with RJ12 ports due to size differences.

What does 8P8C mean for RJ45?

8P8C means eight positions and eight connections, a standard for RJ45.

What is the maximum cable length for RJ45?

The maximum length for standard Ethernet (RJ45) is 100 meters.

Are special tools needed to connect RJ12 or RJ45 connectors?

Yes, crimping tools are needed to connect these connectors to cables.

Is RJ45 suitable for all types of Ethernet?

RJ45 is suitable for most types of Ethernet, including Cat5, Cat6, and others.

How does RJ12 fit into modern communication technology?

RJ12 is less prevalent in modern digital communication, replaced largely by digital and VoIP systems.

Is there a difference in the quality of RJ12 and RJ45 cables?

The quality depends on the specification and manufacturing, not just the type of connector.

What types of devices use RJ45 connectors?

Devices like routers, computers, and network switches use RJ45 connectors.

Are RJ12 and RJ45 visually different?

Yes, RJ45 is larger and has more pins than RJ12.

Can RJ45 be used for telephones?

RJ45 is not typically used for standard telephone connections.

Can I convert an RJ12 connector to RJ45?

Adapters are available, but they don't convert the signal type.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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