Ethernet T568A/B Pinout
RJ-45 pin colour assignments for T568A and T568B.
Overview
The Ethernet T568A/T568B Pinout shows the colour assignment for each of the eight pins on an RJ-45 plug under both the T568A and T568B wiring standards. Each row pairs the pin number with the wire colour, the pair number and the signal carried (TX+, TX−, RX+, RX−) so you can wire a cable, debug a punch-down or build a crossover with confidence.
This is for network installers crimping patch cables, IT generalists chasing intermittent connections and home-lab enthusiasts terminating a wall jack. Long-tail queries it covers include "T568A vs T568B colour code", "RJ-45 pinout for Ethernet", "Cat 6 wiring diagram" and "crossover cable colour order".
How it works
The data is a fixed 8-row table per standard. T568B is the more common choice in the United States and in most modern installations; T568A is required by US government and federal building wiring codes. The two standards differ only in that pairs 2 and 3 are swapped — orange/orange-white and green/green-white change places.
For a straight-through cable, use the same standard on both ends. For a crossover cable (used to directly connect two computers or two switches without auto-MDI-X), use T568A on one end and T568B on the other. Modern devices auto-detect crossover, so this is mostly a legacy concern.
Examples
T568B Pin 1 → white/orange (TX+)
T568B Pin 2 → orange (TX−)
T568B Pin 3 → white/green (RX+)
T568B Pin 6 → green (RX−)
T568A Pin 1 → white/green (TX+)
T568A Pin 2 → green (TX−)
T568A Pin 3 → white/orange (RX+)
T568A Pin 6 → orange (RX−)
Pairs 1 and 4 are identical in both standards (blue + brown).
T568A end + T568B end → crossover cable
FAQ
Should I use T568A or T568B?
T568B is the default for commercial installations in North America. T568A is required for US federal projects and is also used for residential wiring. Pick one and use it consistently across the whole network.
Do I need a crossover for gigabit?
No. Gigabit Ethernet uses all four pairs and requires auto-MDI-X support, which all gigabit switches and cards include. Crossover cables are unnecessary for any modern gigabit-capable equipment.
What is the blue pair used for?
Pair 1 (blue and white/blue) is unused in 10/100 Ethernet but carries one of the four pairs in gigabit Ethernet. Some installations also use it for analogue phone over the same jack.
Why is the pair order in the connector "split"?
Pair 3 (green) is split around pair 1 (blue) to maintain near-end crosstalk performance and match the original phone-line geometry that RJ-45 inherited from RJ-11.
Can I mix T568A jacks and T568B patch cables?
No. The wall jack and the patch cable should both follow the same standard, or you create an accidental crossover. Auto-MDI-X usually compensates, but it is not guaranteed.