T568A vs T568B — RJ45 Pinout Chart
Both RJ45 termination schemes from ANSI/TIA-568, pin by pin: the wire color under each, the pair number, and the signal role. Only the orange and green pairs swap between the two — blue and brown sit in the same positions. Use one scheme on both ends, on every cable, across the whole job; in North American commercial work that scheme is almost always T568B.
RJ45 pinout under T568A and T568B
| Pin | T568A wire | T568B wire | Pair (A / B) | 10/100 role |
|---|---|---|---|---|
| 1 | White/Green | White/Orange | 3 / 2 | TX+ |
| 2 | Green | Orange | 3 / 2 | TX− |
| 3 | White/Orange | White/Green | 2 / 3 | RX+ |
| 4 | Blue | Blue | 1 | — |
| 5 | White/Blue | White/Blue | 1 | — |
| 6 | Orange | Green | 2 / 3 | RX− |
| 7 | White/Brown | White/Brown | 4 | — |
| 8 | Brown | Brown | 4 | — |
Which one to use
T568B dominates North American commercial and residential installs, and matching the existing plant beats any other argument — a building wired B stays B. The often-repeated claim that “TIA recommends T568A” is stale: older editions of the standard did, and U.S. federal contracts once required T568A (FIPS 174), but the current TIA-568.2-D generation is neutral. Both schemes are electrically identical in performance; the pairs land on the same pins, just in different colors. The only hard rule is that both ends of a cable — and in practice the whole project — use the same scheme.
Crossover cables — a legacy concern
Terminating one end A and the other end B swaps the transmit and receive pairs — a crossover cable, once required for like-to-like links (switch to switch, PC to PC). Auto MDI-X, standard in effectively all gigabit and newer hardware, detects and corrects pair orientation automatically, so crossover cables are obsolete. If a wiremap test shows pairs 2 and 3 exchanged, treat it as a termination error, not a feature.
Related look-ups: the cable category comparison, the 100 m distance rules, and the RJ11/RJ14/RJ45 connector designations.
Common questions
Should I use T568A or T568B?
For nearly all U.S. commercial and residential work, use T568B — it is the de facto standard and what an existing plant almost certainly follows. Older editions of TIA-568 recommended T568A for new horizontal cabling (and federal work once specified it via FIPS 174), but the current TIA-568.2-D generation treats both as valid. What the standard does require is consistency: the same scheme on both ends of every cable and, in practice, across the whole job. On an existing building, match whatever is already in the walls.
What is the T568B color order?
Pin 1 to pin 8: white/orange, orange, white/green, blue, white/blue, green, white/brown, brown. T568A is the same list with the orange and green pairs exchanged — white/green, green, white/orange, blue, white/blue, orange, white/brown, brown.
What happens if I mix T568A and T568B?
A cable with T568A on one end and T568B on the other is a crossover cable — the transmit and receive pairs trade places. That was once deliberate for switch-to-switch links, but auto MDI-X (standard in virtually all gigabit hardware) made crossover cables obsolete. Today a mixed-scheme termination is simply a wiring error: the link may still work through auto-correction, but it will fail a wiremap certification test.
Do all 8 wires matter?
10BASE-T and 100BASE-TX only use pins 1/2 (transmit) and 3/6 (receive). 1000BASE-T and everything faster transmits and receives on all four pairs simultaneously — all 8 wires must terminate correctly for a gigabit link, which is why a cable that "worked" at 100 Mbps can fail when the switch is upgraded.
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