RJ45 Wiring Color Code Guide

Pin-by-pin wire colors for T568A and T568B Ethernet standards. Includes straight-through vs crossover reference and the 10/100 Mbps pin function table.

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.
What's the difference between T568A and T568B?
The only difference is that the orange and green wire pairs are swapped. T568B has orange-white on Pin 1; T568A has green-white on Pin 1. Both work identically for data. T568B is more common in US commercial installations; T568A is preferred in residential and some international standards. Pick one standard and use it consistently throughout your infrastructure.
When do I need a crossover cable?
Crossover cables connect same-type devices directly (computer-to-computer, switch-to-switch) by crossing TX and RX signals. However, virtually all modern networking equipment (since ~2008) supports Auto-MDIX, which automatically detects cable type and adjusts. With Auto-MDIX, straight-through cables work for all connections. Crossover cables are mainly needed for older equipment or specific direct-connection scenarios.
What are the 8 pins on an RJ45 connector used for?
Pins 1 and 2: TX+ and TX− (transmit data). Pins 3 and 6: RX+ and RX− (receive data). Pins 4, 5, 7, 8: unused for 10/100 Mbps data but may carry PoE power or phone. Gigabit Ethernet (1000BASE-T) uses all four pairs bidirectionally. The wire colors for T568B: 1=White/Orange, 2=Orange, 3=White/Green, 4=Blue, 5=White/Blue, 6=Green, 7=White/Brown, 8=Brown.
How far can I untwist the wires when making an RJ45 cable?
Keep untwisted wire to a maximum of 0.5 inches (13mm) at the connector. The twists in each pair are critical for canceling electromagnetic interference and crosstalk between pairs. Untwisting too much degrades signal quality, especially at higher speeds (Cat6/Cat6a). Always maintain the twist as close to the connector as possible, and use the correct category-rated connectors for your cable type.

How to Use the RJ45 Wiring Guide

  1. Select your wiring standard — T568A (green-white on pin 1) or T568B (orange-white on pin 1), the more common standard in the US.
  2. Reference the color code chart — see the exact wire color for each of the 8 pin positions (1–8).
  3. Determine cable type — straight-through (both ends same standard) for connecting different device types, or crossover (T568A one end, T568B other) for same-device connections.
  4. Use the pin function table to understand which pins carry TX+, TX−, RX+, and RX− signals.
  5. Verify your wiring with a cable tester before deploying in production networks.

Understanding RJ45 Wiring Standards and Pinouts

The RJ45 connector (technically 8P8C — 8 Position 8 Contact) is the standard connector for Ethernet networking, terminating twisted-pair cables (Cat5e through Cat8). Two wiring standards defined by TIA/EIA-568 govern the color-to-pin assignment: T568A and T568B. The difference is simply that the orange and green pairs are swapped. T568B is more common in the United States and commercial installations, while T568A is more common in residential and some international installations. Either standard works — what matters is consistency within a single cable and infrastructure.

For T568B (the dominant standard), the pin assignments from left to right (clip facing down) are: Pin 1 = White/Orange (TX+), Pin 2 = Orange (TX−), Pin 3 = White/Green (RX+), Pin 4 = Blue, Pin 5 = White/Blue, Pin 6 = Green (RX−), Pin 7 = White/Brown, Pin 8 = Brown. Pins 1, 2, 3, and 6 carry the active data signals for 10/100 Mbps Ethernet (100BASE-T). Gigabit Ethernet (1000BASE-T) uses all four pairs bidirectionally. The blue and brown pairs (Pins 4, 5, 7, 8) carry no data in 10/100 but may support PoE power or phone lines.

Straight-through cables use the same standard (T568A or T568B) on both ends and connect different device types — e.g., computer to switch, router to switch. Crossover cables use T568A on one end and T568B on the other, connecting the TX pins on one device to the RX pins on another. They're needed for same-type connections (computer-to-computer, switch-to-switch) without auto-MDIX. Modern switches and NICs support Auto-MDIX, which automatically detects and adjusts for cable type, making crossover cables largely unnecessary since 2008. When making cables, maintain the twist as close to the connector as possible (untwist no more than 0.5 inches / 13mm) to minimize crosstalk.

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