Two standards, endless confusion. The difference between T568A and T568B is tiny, but mixing them inside one building causes real troubleshooting pain. Here is the clear answer.
Technical AnshuT568A and T568BStraight Through
Watch the full RJ45 crimping guide on video - every step shown live, from stripping the cable to the final tester check
Ask ten installers and you will hear strong opinions about A versus B - but the engineering truth is calmer. Both standards perform identically. The only real rule is consistency: same standard at both ends of a cable, and one standard across a whole site.
T568A Pinout - Pins 1 to 8
Pin 1White-Green
Pin 2Green
Pin 3White-Orange
Pin 4Blue
Pin 5White-Blue
Pin 6Orange
Pin 7White-Brown
Pin 8Brown
T568A swaps the orange and green pairs compared to T568B. Same pairs, same positions for blue and brown - only the two data pairs trade places.
1
What Actually Differs Between A and B
Both standards arrange the same four twisted pairs on the same eight pins. The only difference: T568B puts the orange pair on pins 1-2 and the green pair on pins 3-6; T568A does the reverse. The blue pair always sits on pins 4-5 and the brown pair on pins 7-8. Electrically the two are equal. Neither is faster, cleaner or more modern.
2
The Only Rule That Matters - Be Consistent
Both ends of one cable in the same standard = a straight-through cable. This is what PCs, cameras, printers and switches use
In a building, pick ONE standard for every jack, patch panel and patch lead. Mixed standards across a site create confusion that wastes hours later
When you repair someone else's wiring, match what is already there. Check the existing jack or plug first and copy its standard
3
The Crossover Truth for Modern Gear
One end A and one end B makes a crossover cable, which old equipment needed to connect two similar devices directly. Almost everything made in the last two decades has Auto MDI-X - the port detects and adjusts itself. Gigabit Ethernet builds this in by design. So a crossover cable is rarely needed today, and a straight-through cable of either standard will work between two PCs. Honest bottom line: if you accidentally make a crossover, modern devices will very likely still link fine - but build straight-through on purpose, so the next technician is not confused.
4
Which One Should You Choose
New home or small office wiring: T568B - it matches most ready-made patch leads and most installers' habit
Government and some large structured-cabling contracts specify T568A - follow the project document if there is one
Extending or repairing existing wiring: match the site, even if it is A. Consistency beats preference
Honest note: anyone claiming T568B is "faster" than T568A is selling something. The difference is pair placement on two pairs only. What decides performance is crimp quality, untwist length and cable quality - not the letter.
Watch the Full RJ45 Crimping Video
See the crimping technique live on camera - wire order, seating depth and tester reading, exactly as done in this guide.
What happens if one end is T568A and the other is T568B?
You get a crossover cable. Old devices needed that for PC-to-PC links. Modern ports with Auto MDI-X - including all gigabit ports - adjust automatically, so it will usually still work, but it is not the correct way to build a patch lead.
My wall jacks are T568A. Should I redo them as B?
No. If the whole site is consistently A, it is a correct installation. Only match new work to the existing standard. Redoing working jacks wastes plugs and risks introducing faults.
Is T568B compulsory for gigabit and PoE?
No. Gigabit and PoE work on either standard because the pairs land on the same pins - only the orange and green pair colours trade positions. What matters is that all four pairs are continuous and correctly paired.
This guide is based on the Technical Anshu RJ45 crimping video • Stuck on any step? Ask in the video comments - you will get a reply there