RJ45 T568A / T568B Wiring Color Code Guide

Pin 1 is on the left when viewing the connector from the front (contacts facing you, clip pointing down). T568B is the most common scheme for patch cables in North America; T568A is preferred in residential and government installations per TIA/EIA-568.

Pin Function Reference

For 10BASE-T and 100BASE-TX Ethernet, only pins 1, 2, 3, and 6 are used. Pins 4, 5, 7, 8 are reserved (or used for PoE power pairs). 1000BASE-T (Gigabit) uses all four pairs in both directions.

Pin	Function (10/100)	T568A Wire	T568B Wire	Pair
1	TX+ Transmit +	White / Green	White / Orange	2
2	TX− Transmit −	Green	Orange	2
3	RX+ Receive +	White / Orange	White / Green	3
4	— (unused / PoE +)	Blue	Blue	1
5	— (unused / PoE +)	White / Blue	White / Blue	1
6	RX− Receive −	Orange	Green	3
7	— (unused / PoE −)	White / Brown	White / Brown	4
8	— (unused / PoE −)	Brown	Brown	4

Straight-Through vs Crossover

A cable's ends determine its type. Most modern Ethernet interfaces have Auto-MDIX, which makes crossover cables largely obsolete, but they remain essential for direct device-to-device links on legacy hardware.

Straight-Through Cable

Both ends use the same standard (T568B–T568B or T568A–T568A). Used to connect different device classes.

End A: 1↔1, 2↔2, 3↔3, 6↔6
End B: identical mapping

Use: PC ↔ switch, router ↔ switch, PC ↔ wall jack

Crossover Cable

One end is T568A, the other is T568B. The TX and RX pairs are swapped so two devices of the same class can talk directly.

End A (T568A): TX on 1/2, RX on 3/6
End B (T568B): TX on 3/6, RX on 1/2

Use: PC ↔ PC, switch ↔ switch, router ↔ router

Auto-MDIX (IEEE 802.3ab) automatically detects the required cable type and swaps TX/RX internally. All Gigabit and newer interfaces support it, so a straight-through T568B cable works for almost every modern link.

FAQ

What is the difference between T568A and T568B?

The only difference is the assignment of the orange and green pairs. In T568B, pins 1 and 2 carry the orange pair (white-orange / orange) and pins 3 and 6 carry the green pair. In T568A, those two pairs are swapped: green goes on 1/2 and orange on 3/6. The blue and brown pairs are wired identically in both standards.

Which standard should I use?

T568B is the most common choice for commercial patch cables in the United States and is what most pre-made cables use. T568A is required for U.S. government contracts and is preferred in residential wiring. The key rule: both ends of a straight-through cable must use the same standard. Mixing them on one cable makes a crossover cable.

Why are the wires on pins 3 and 6 not adjacent?

Pins 3 and 6 carry one differential pair (the green pair in T568B). They are split across the connector so that pair 2 (blue, pins 4/5) sits physically between them. This layout preserves backwards compatibility with older one-pair and two-pair telephone wiring on the same 8P8C connector.

Do I need a crossover cable anymore?

Usually no. Auto-MDIX, introduced with 1000BASE-T (Gigabit Ethernet), automatically detects cable type and swaps transmit and receive internally. Nearly every modern NIC, switch, and router supports it, so a straight-through T568B cable works for direct PC-to-PC links. Crossover cables are still useful for older 10/100 hardware or console/management ports.

What does "white/orange" actually look like?

Each twisted pair shares a color. One wire is solid (or mostly solid) — e.g. solid orange — and its partner is predominantly white with an orange stripe. The striped wire is shown in tables as "White / Orange" or sometimes "W-O" / "W/Or". In the diagrams above, striped wires are shown with a hatch pattern over the white base.

Is RJ45 the same as 8P8C?

Strictly speaking, RJ45 refers to a specific registered-jack wiring scheme (RJ45S) from the old Bell System. The physical connector used for Ethernet is technically an 8P8C (8-position, 8-contact) modular plug. The terms are used interchangeably in everyday networking, and this page follows that convention.

RJ45 Wiring Color Code Guide

Pin Function Reference

Straight-Through vs Crossover

Straight-Through Cable

Crossover Cable

FAQ

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