The only difference is that the green pair and the orange pair swap places. T568A puts green on pins 1 and 2; T568B puts orange there. Pins 4, 5, 7 and 8 are identical. Performance is identical too, so the real requirement is using one standard consistently.
- Only pins 1, 2, 3 and 6 differ between the two standards
- Both are in the same TIA document, as alternatives
- T568B dominates North American commercial work
- T568A is usual on US federal projects and outside North America
- A cable with one of each end is a crossover cable
On this page
The pinoutsThe two pinouts, side by side
Eight wires, four twisted pairs, one RJ45 connector. Both wiring standards use the same cable and the same connector, and both put the blue pair on pins 4 and 5 and the brown pair on pins 7 and 8.
T568A, pin by pin:
| Pin | Wire color | Pair |
|---|---|---|
| 1 | White with green stripe | Pair 3 |
| 2 | Green | Pair 3 |
| 3 | White with orange stripe | Pair 2 |
| 4 | Blue | Pair 1 |
| 5 | White with blue stripe | Pair 1 |
| 6 | Orange | Pair 2 |
| 7 | White with brown stripe | Pair 4 |
| 8 | Brown | Pair 4 |
T568B, pin by pin:
| Pin | Wire color | Pair |
|---|---|---|
| 1 | White with orange stripe | Pair 2 |
| 2 | Orange | Pair 2 |
| 3 | White with green stripe | Pair 3 |
| 4 | Blue | Pair 1 |
| 5 | White with blue stripe | Pair 1 |
| 6 | Green | Pair 3 |
| 7 | White with brown stripe | Pair 4 |
| 8 | Brown | Pair 4 |
Read the two tables together and the whole of T568A vs T568B is four rows. Pins 1, 2, 3 and 6 carry orange wires in one standard and green wires in the other. Pins 4, 5, 7 and 8 do not move.
That structure is not an accident. Pins 1 and 2 are one pair and pins 3 and 6 are another, which looks strange until you notice that pins 4 and 5 sit between them and carry a pair of their own.
The RJ45 connector was laid out so that a two pair telephone jack could be plugged into the middle of it and still work, and everything about the ordering of the wires follows from that constraint.
Why two existWhy there are two standards at all
The split is historical rather than technical, and knowing the history is the fastest way to remember which is which.
T568A follows the older telephone wiring scheme. In the residential wiring schemes that preceded structured network cabling, the first pair sat on the middle two pins and the second pair straddled it.
T568A keeps that arrangement intact, which means a single line or two line telephone jack wired to the same punch down still works. Backward compatibility with voice wiring is the entire argument for T568A.
T568B follows the AT&T 258A convention, which was already in wide use in commercial buildings when the standard was written. Rather than force an industry to rewire, the standard admitted both.
The result is that the TIA standard contains both RJ45 pinouts, describes them as alternatives, and the professional network installation world settled the question by region and by sector rather than by merit.
North American commercial work leans heavily to T568B. US federal projects and a great deal of work outside North America use T568A. Neither community is wrong.
Which to pickDoes it matter which one you use
For the electrical performance of the cable, no. For the building, yes, and the reason is consistency rather than physics.
Ethernet performance is identical. Both wiring standards put a pair on pins 1 and 2 and a pair on pins 3 and 6, both keep the wires twisted right up to the connector, and both pass the same certification against the same category limits. A properly terminated T568A cable and a properly terminated T568B cable test the same.
Consistency is what actually matters. A network where some outlets are wired T568A and some T568B works fine until somebody makes a patch cable, tests a run, or traces a fault, and then every assumption is wrong. The cost of mixing the two standards is not a broken network, it is an installation nobody can reason about.
Follow what is already there. In an existing network, the wiring standard already in the patch panel is the correct answer, whatever it is. Opening a jack and reading the color code on the wires takes a minute and settles it.
When there is nothing to follow. Pick T568B for commercial work in North America, because it is what the next technician will expect. Pick T568A if the specification says so, which is usual for federal projects, or if the site already uses it.
Mismatched endsWhat happens when the ends do not match
A cable terminated T568A at one end and T568B at the other is a crossover cable. Pins 1 and 2 at one end land on pins 3 and 6 at the other, which is exactly what a crossover does.
For twenty years that mattered on every Ethernet network, because connecting two computers directly, or two switches, needed a crossover cable while everything else needed a straight through cable. Getting it backward meant no link light at all.
It stopped mattering with Auto MDI-X, which lets a port detect which pair is receiving and swap internally. It is optional in 100BASE-TX and mandatory in 1000BASE-T, so any gigabit port has it, and in practice both cables now work between any two modern devices.
That does not make a mixed cable acceptable. It makes the mistake silent, which is worse. A mismatched cable in a patch panel works, tests as a crossover if anybody checks, and confuses the next person who traces it. Older or simpler equipment, some industrial gear and some management ports, still lacks Auto MDI-X and will not link at all.
Split pairsThe mistake that a cheap tester passes
There is one wiring error worth naming separately, because it is the one that hides.
A basic continuity tester checks that pin 1 connects to pin 1, pin 2 to pin 2, and so on. It says nothing about which wires are twisted together.
Wire pins 1 and 2 with one wire from the orange pair and one from the green pair, and every pin still maps to the right pin. The tester lights all eight in order and reports a pass.
That fault is a split pair. The signal now travels on two wires that are not twisted around each other, so the noise cancellation that makes twisted pair Ethernet work is gone. The link often comes up, runs at a lower speed than it should, drops under load, or fails only when the neighboring cable is busy.
Two things prevent it. Terminate by following the color code exactly rather than by matching pin to pin, and use a tester that measures crosstalk rather than continuity when the cable matters.
PitfallsWhere people go wrong
Mixing the two wiring standards in one network. The most common mistake and the most expensive to unpick, because nothing fails immediately and the inconsistency is discovered years later during a fault.
Believing one is faster. Neither is. Both carry gigabit Ethernet and both carry 10 gigabit on cable rated for it. The choice between the standards is a convention, not a specification of network performance.
Untwisting too much at the connector. The standard allows about half an inch of untwist for Category 5e and less for Category 6. Stripping back an inch and fanning the wires out flat is the usual reason a run fails certification, and it happens with either wiring standard.
Wiring a jack to match the RJ45 plug it faces. Jacks and plugs are numbered in opposite directions when you hold them the obvious way. Follow the color code printed on the jack rather than trying to reason about which wires land where.
Assuming a crossover cable is still needed. Auto MDI-X handles it on any gigabit port, and deliberately making crossover cables is now a way to create confusing inventory.
Trusting a continuity tester. It confirms the pins line up and cannot detect a split pair, which is the fault most likely to produce a link that works badly rather than not at all.
Using flat or untwisted network cable. The twist in the wires is the entire mechanism. Cable without it will terminate to either standard perfectly and still fail at any real distance.
ComparisonEvery row that measures performance says the same thing
| Criterion | T568A | T568B |
|---|---|---|
| Pins 1 and 2 | Green pair | Orange pair |
| Pins 3 and 6 | Orange pair | Green pair |
| Pins 4, 5, 7 and 8 | Identical | Identical |
| Maximum speed supported | Same | Same |
| Certification results | Same | Same |
| Compatible with older voice wiring | Yes | No |
| Common in US commercial work | Less | More |
| Usual for US federal projects | Yes | Less |
| Common outside North America | Yes | Less |
Every row that measures performance says the same. Every row that differs is about convention and history, which is why T568A vs T568B is a decision for whoever documents the network rather than for whoever crimps the RJ45.
FAQFrequently asked questions
What is the difference between T568A and T568B?
The green pair and the orange pair swap positions. T568A puts green on pins 1 and 2 and orange on pins 3 and 6; T568B does the reverse. Pins 4, 5, 7 and 8 are the same in both.
Is T568A or T568B better?
Neither. They perform identically and pass the same tests. The only real consideration is using one standard consistently throughout a building.
Which wiring standard is more common?
T568B on North American commercial networks. T568A is usual for US federal projects and common in much of the rest of the world.
Can I use T568A on one end and T568B on the other?
That produces a crossover cable. Modern gigabit ports handle it because Auto MDI-X is mandatory in 1000BASE-T, but it will confuse whoever traces the cable later, and older equipment may not link at all.
Do I still need crossover cables?
No, on anything with a gigabit port. Auto MDI-X detects and corrects the orientation, so a straight through cable connects two switches or two computers directly.
What are the T568B colors in order?
White with orange stripe, orange, white with green stripe, blue, white with blue stripe, green, white with brown stripe, brown.
What are the T568A colors in order?
White with green stripe, green, white with orange stripe, blue, white with blue stripe, orange, white with brown stripe, brown.
Why are pins 3 and 6 the same pair?
Because pins 4 and 5 carry a pair between them. The RJ45 layout was chosen so a two pair telephone jack could be plugged into the middle of the connector and still work, which is a backward compatibility decision rather than a network one.
Does the standard matter for Power over Ethernet?
No. Power over Ethernet uses the pairs regardless of which color occupies them, and both wiring standards deliver it identically.
What is a split pair and why does it matter?
A termination where the pins are correct but the conductors come from different twisted pairs. A continuity tester passes it, the noise cancellation is gone, and the link works badly rather than failing outright.
Which standard should I use in a house?
Whichever is already in the panel. For new residential work either is fine, and T568A has a small advantage if any telephone wiring remains in service.
Does the choice affect Cat6 or Cat6a cable?
No. The category of the cable describes the copper and the components; the wiring standard describes which color lands on which pin. They are independent choices.
Can I re-terminate one end to change the standard?
Yes, and it is the correct fix for a cable that was made with mismatched ends. Cut the connector off, re-terminate it to match the other end, and test.
Keep readingRelated concepts
Read next · Cabling and connectivity Cat6 vs Cat6a The category describes the cable and the components, and the wiring standard describes which color lands on which pin. Open this next10 min- Diagnostics · 11 min Ping and Traceroute A split pair produces a link that works badly rather than not at all, which is exactly the symptom these two tools are used to chase.
- Switching · 11 min Spanning Tree Protocol A cable made as a crossover by accident is one of the ways a loop gets built between two switches.
- Cabling and connectivity · 9 min What UTP Cable Is, and Why the Twist Does the Shielding How it gets terminated.