A registered jack (RJ) is a standardized network interface for connecting voice and data telecommunications equipment. Although the specification includes physical construction, wiring, and signal semantics, the terms are often used loosely to refer to the modular connectors. So this comparison focuses on the modular connectors used in RJ11 and RJ45 jacks.
RJ11 is the most widely-used registered jack in telecommunications. RJ11 has a 6P2C or 6P4C configuration, and is used for wiring a single phone line. RJ45 uses an 8P8C configuration. In fact, the RJ45(S) jack — as defined in the standardized spec — is rarely used, but the RJ45 commonly refers to any 8P8C modular connector used in computer networking (Ethernet). It is this meaning of RJ45, the modular connector, that is being compared here. The specification that RJ45 in ethernet adheres to is called the TIA/EIA-568.
Comparison chart
 | RJ11 | RJ45 |
|---|---|---|
| Configuration | 6P4C (6 positions, 4 connectors) | 8P8C (8 positions, 8 connectors) |
| Usage | Phones, ADSL lines, modem cables. RJ11 is mostly used for voice applications. | Computer networking. RJ45 is used in Ethernets or connecting cable modems with Wi-Fi routers. |
| Bandwidth | RJ11 connectors can support about 24Mbps | RJ45 connectors can support 10Gbps over Ethernet, provided the other equipment like network cables also support that speed. |
| Shape and size | Compact, square-shaped | Longer, more rectangular |
Appearance
RJ45 plugs are long and rectangular, with a width of just under 11.65mm. RJ11 plugs are square and shorter, with a width of 9.65mm. Here are some pictures of RJ45 and RJ11 connectors and jacks:
RJ11 and RJ45 combo modular jack |
Schematic of RJ11 plug and jack |
Schematic of RJ45 plug and jack |
RJ11 connector |
RJ45 connector |
RJ45 jack |
RJ45 connector plug |
Configuration and Usage
As shown in the schematic above, RJ45 uses an 8P8C configuration, which means 8 Positions and 8 Contacts (or connectors, or conductors). Using 8 contacts allows for greater bandwidth so RJ45 is used for data-intensive applications like Ethernet and can support bandwidth up to 10Gbps. Overall bandwidth is, of course, contingent upon what other components of the network such as cabling or routers can support. RJ45 is also sometimes used for VOIP phones in offices.
RJ11 is used for connecting single phone lines and uses a 6P2C or 6P4C configuration. With only 2 of the 6 available connection points, the RJ11 plug supports limited-bandwidth applications. This includes phone lines and ADSL connections.
Other types of RJ connectors
RJ11 is the most widely-used connector, followed by RJ14, and RJ25. All three jack types are used to connect phones—for one-, two-, and three-line service respectively. These are all modular connectors with 6 available positions. The RJ11 technically uses the center 2 contacts of 6 available, and is used for wiring a single phone line. RJ14 is similar to RJ11 but is wired for two phone lines; it uses a 6P4C configuration where 4 connectors out of the 6 positions are used. RJ25 uses all 6 of the available positions (6P6C) and is able to connect 3 lines. RJ61 is a similar registered jack for 4 lines; it uses an 8P8C configuration similar to the RJ45.
RJ22, also called an RJ10, is the smallest of the modular plugs. It has a 4P4C configuration and is used in handset cords. It is not an official ACTA (Administrative Council for Terminal Attachments) specification.
RJ12 connectors are also similar to RJ11 but have a 6P6C configuration. They are used to connect a phone line with the key telephone system, small exchange-like systems used by businesses to connect to the carrier on the outside and create a network of phones and extensions on the inside. RJ12 connectors can be used in place of RJ11 because RJ12 has all the connectors RJ11 needs (plus 4 extra).
References
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