RJ11 ⇔ RJ45 | Technical Characteristics | instrumentic.info

an adapter RJ11 to RJ45
an adapter RJ11 to RJ45

RJ11 ⇔ RJ45

This adapter consists of an RJ45 network socket and an RJ11 socket for the landline. These two sockets are not physically compatible but electrically.


The telephone cable that arrives at the subscriber's home is called RJ11, Registered Jack 11, it has 4 conductors grouped into 2 colored pairs. The socket consists of 6 physical positions and 4 electrical contacts of which only 2 are used (6P2C).
These two central contacts are used for the telephone line.

RJ45 Registered Jack 45 has 8 positions and 8 electrical contacts (8P8C), this connector is commonly used for Ethernet connections, i.e. networks, especially to connect computers to the Internet.
The right RJ45 cable is used to connect a computer to a Hub or Switch. The cross-wire RJ45 cable is usually used to connect two Hubs or two Switches or two computers.

wiring RJ11 to RJ45
wiring RJ11 to RJ45

Compatibility between RJ11 and RJ45

All strands of RJ-type cables go in pairs and are twisted together along the entire length of the sheath, this technique is used to improve signal quality.

Most wired Ethernet network communications are routed on a Category 5 or Category 6 RJ45 cable with a modular 8P8C plug at each end.
The RJ11 telephone cable that arrives at the subscriber has 4 contactors in a modular 6P2C card. Only the two central contactors are used for the line.

Warning : mechanically the male RJ11 connector does not fit into the female RJ45 connector because of the thick right and left edges.

The RJ45 connector has 8 positions :

Position TWISTED PAIR COLOR TWISTED PAIR NUMBER
1 WHITE / GREEN 3
2 Green 3
3 ORANGE WHITE 2
4 Blue 1
5 WHITE/BLUE 1
6 Orange 2
7 WHITE / BROWN 4
8 Brown 4

The RJ11 connector has 6 positions :

Position R/T TWISTED PAIR COLOR TWISTED PAIR NUMBER
1 T WHITE / GREEN 3
2 T WHITE / ORANGE 2
3 R Blue 1
4 T WHITE/BLUE 1
5 R Orange 2
6 R Green 3

wiring RJ45 to RJ11
wiring RJ45 to RJ11

Connection RJ11 to RJ45

To connect these two elements we use an adapter that requires no power and guarantees physical and electrical compatibility. These adapters are easily found on the internet and are cheap. You can also make this type of adapter yourself.

On the RJ11 socket, the two contacts of the center, numbered 2 and 3, are used as a telephone line, they correspond to the twisted pair 1 of blue and white/blue color.

On an RJ45 socket, during a 10/100 Mbps computer wiring, only the four 1-2 and 3-6 pins are used to transmit the information. During a computer wiring in 1000 Mbps, the 8 pins are used
For the telephone connection it is the two contacts of the center, numbered 4 and 5 of the twisted pair 1, blue and white/blue, of the RJ45 that serve.

Electrical adaptation between RJ11 and RJ45

Position RJ45 Position RJ11 RJ11 twisted pair no. Number for wiring at RJ45 RJ45 twisted pair number
1 3
2 1 3 3
3 2 2 7 2
4 3 1 4 1
5 4 1 5 1
6 5 2 8 2
7 6 3 4
8 4

wiring RJ45 to T or gigogne
wiring RJ45 to T or gigogne

RJ45 to a T

In France and in countries that have installed T or gigogne sockets as wall sockets, the two central contacts 4 and 5 of the RJ45 socket must lead to contacts 1 and 3 of the T socket that correspond to line 1.

You should know that France Télécom recommends the use of the star-connected RJ45 for new telephone facilities, instead of the T, since 2003.

Adapter DIY

It is possible to make your own adapter RJ11 RJ45 as shown in this video Youtube.