T568A vs T568B: RJ-45 Wiring Color Order Explained
T568A and T568B are the two wiring standards for terminating an RJ-45 connector on a twisted-pair Ethernet cable. They are a CompTIA A+ Core 1 favorite because the question is concrete: which color wire goes on which pin? The good news is that the two standards are almost identical — only two pairs swap — so once you learn one, you effectively know both. This guide gives you the exact pinout for each, explains crossover cables and auto-MDIX, and lets you test yourself with free questions.
T568A vs T568B pinout table
Pin numbers read left-to-right with the connector's tab facing down and the gold contacts facing you.
| Pin | T568B | T568A |
|---|---|---|
| 1 | White/Orange | White/Green |
| 2 | Orange | Green |
| 3 | White/Green | White/Orange |
| 4 | Blue | Blue |
| 5 | White/Blue | White/Blue |
| 6 | Green | Orange |
| 7 | White/Brown | White/Brown |
| 8 | Brown | Brown |
The one difference that matters
The only change between the two standards is that the orange pair (pins 1 and 2) and the green pair (pins 3 and 6) are swapped. The blue and brown pairs sit on pins 4/5 and 7/8 in both standards and never move. So if you memorize T568B as "orange, green, blue, brown" with the striped wire first on each pair, you can derive T568A simply by trading orange and green.
Straight-through vs crossover cables
A straight-through cable uses the same standard on both ends — typically T568B to T568B — and connects pin 1 to pin 1, pin 2 to pin 2, and so on. It is used between unlike devices, such as a PC to a switch or a switch to a router. A crossover cable uses T568A on one end and T568B on the other, which crosses the transmit and receive pairs. It was used between like devices — switch-to-switch, PC-to-PC, or router-to-router. The CompTIA exam still expects you to recognize the crossover pinout even though modern hardware has largely removed the need.
Auto-MDIX
Auto-MDIX (automatic medium-dependent interface crossover) is a feature of gigabit interfaces that detects the required cable connection and internally swaps transmit and receive as needed. With Auto-MDIX, a straight-through cable works for almost every connection, so crossover cables are rarely required in practice. For the exam, know that Auto-MDIX exists and that it eliminates the need to choose between straight-through and crossover cables on supported hardware.
Memory tips
- T568B = "Orange starts." The orange pair goes on pins 1 and 2.
- T568A = "Green starts." The green pair goes on pins 1 and 2.
- Both read "white first, then solid" on each active pair (White/Orange, Orange).
- The pair order in T568B is Orange, Green, Blue, Brown — think of it as the colors getting darker as you go.
- Same standard both ends = straight-through; different standards = crossover.
Try 3 free sample questions
Questions are visible below. Pick an answer to reveal the correct one and the explanation.
Q1.In the T568B standard, which color wire goes on pin 1?
Q2.What kind of cable do you create by wiring one end T568A and the other end T568B?
Q3.Which pairs differ between T568A and T568B?
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Frequently asked questions
Which standard should I use, T568A or T568B?
In the United States, T568B is the most common for commercial and residential wiring. T568A is sometimes required by government contracts and is more common in some other countries. The important rule is to use the same standard on both ends of a straight-through cable, and to follow your organization's existing standard for consistency.
What is the difference between a straight-through and a crossover cable?
A straight-through cable uses the same standard (e.g. T568B) on both ends, connecting pin 1 to pin 1, and is used to connect unlike devices such as a PC to a switch. A crossover cable uses T568A on one end and T568B on the other, crossing the transmit and receive pairs, and was used to connect like devices such as switch-to-switch or PC-to-PC.
Does auto-MDIX make crossover cables obsolete?
Largely yes. Auto-MDIX (automatic medium-dependent interface crossover) lets modern gigabit ports detect the cable and adjust transmit and receive automatically, so a straight-through cable works for most connections. CompTIA still expects you to know crossover cable wiring for the exam.
Why are pins 3 and 6 not adjacent on the connector?
Pins 1 and 2 form one twisted pair (transmit) and pins 3 and 6 form another (receive). The split placement keeps the correct wire pairs together for the Ethernet pinout while preserving the twisted-pair geometry that cancels crosstalk.