Understanding the RJ45 pinout is essential for anyone working with Ethernet networking, from PCB design engineers to cable installation technicians. The RJ45 connector uses an 8-position, 8-contact (8P8C) modular jack, and its pinout determines how data signals travel between networked devices. Two wiring standards govern this pinout: T568A and T568B. While both support the same Ethernet speeds, the difference lies in the color-coded wire-to-pin assignment. This guide provides a complete RJ45 wiring diagram, explains the T568A vs T568B distinction, and covers crossover vs straight-through cable configurations — all critical knowledge for designing and maintaining reliable network connections.
Whether you are designing a network switch motherboard, specifying connectors for an industrial gateway, or wiring a data center rack, getting the RJ45 pinout right is non-negotiable. A single swapped pair can cause intermittent connectivity, signal degradation, or complete link failure. As Ethernet speeds increase from 1G to 10G and beyond, correct pinout and wire pair twisting become even more critical for maintaining signal integrity.
This guide is written for hardware engineers, PCB designers, and network technicians who need authoritative, practical information about RJ45 pinout standards. VITALCONN Electronics manufactures RJ45 connectors with integrated magnetics and discrete options — see our Ultimate Guide to RJ45 Connectors for a complete product overview — and this guide draws on our engineering team's field experience to address the most common pinout questions.
RJ45 Pinout Diagram: T568A vs T568B Color Code Assignments
The RJ45 connector has 8 pins, numbered 1 through 8 when looking at the connector from the front (contact side facing you, tab pointing down). Each pin is assigned a specific wire color under the TIA/EIA-568 standard. Below is the complete RJ45 pinout for both T568A and T568B:
| Pin # | T568A Color | T568B Color | Signal (T568B) | Pair # |
|---|---|---|---|---|
| 1 | White/Green | White/Orange | TX+ (Transmit +) | Pair 2 |
| 2 | Green | Orange | TX- (Transmit -) | Pair 2 |
| 3 | White/Orange | White/Green | RX+ (Receive +) | Pair 3 |
| 4 | Blue | Blue | Blue Pair (PoE+) | Pair 1 |
| 5 | White/Blue | White/Blue | Blue Pair (PoE-) | Pair 1 |
| 6 | Orange | Green | RX- (Receive -) | Pair 3 |
| 7 | White/Brown | White/Brown | Brown Pair (PoE+) | Pair 4 |
| 8 | Brown | Brown | Brown Pair (PoE-) | Pair 4 |
Key observations from this pinout table:
- Pins 1 and 2 are always a differential pair (transmit in T568B)
- Pins 3 and 6 are always a differential pair (receive in T568B)
- Pins 4, 5, 7, and 8 are used for Power over Ethernet (PoE) in Mode B (phantom power on spare pairs)
- The only difference between T568A and T568B is that the Orange and Green pairs are swapped
T568A vs T568B: Which Standard Should You Use?
The difference between T568A and T568B is purely the color-to-pin assignment. Electrically, both standards carry Ethernet signals identically — the data reaches the same pins on the RJ45 connector regardless of which color code is used. The critical rule is consistency: both ends of a straight-through cable must use the same standard.
T568B is the most commonly used standard in the United States and in commercial installations worldwide. T568A is more common in residential wiring and is the preferred standard for U.S. government contracts. From a technical standpoint, there is no performance difference between the two.
| Aspect | T568A | T568B |
|---|---|---|
| Pair 2 (Pins 1,2) | Green pair | Orange pair |
| Pair 3 (Pins 3,6) | Orange pair | Green pair |
| Performance | Identical to T568B | Identical to T568A |
| Common Usage | Residential, U.S. government | Commercial, most common globally |
| Standard Origin | Original AT&T 258A color code | ANSI/TIA-568 commercial standard |
| Compatibility | Compatible with T568B (both ends must match) | Compatible with T568A (both ends must match) |
RJ45 Wiring Diagram: Straight-Through vs Crossover Cables
Two cable types use the RJ45 pinout: straight-through and crossover. Understanding the difference is critical for proper network connectivity.
A straight-through cable uses the same wiring standard (either T568A or T568B) on both ends. This is the standard cable for connecting different device types — for example, a computer to a switch, or a router to a switch.
A crossover cable uses T568A on one end and T568B on the other. This swaps the transmit and receive pairs, allowing two devices of the same type (such as two computers or two switches) to communicate directly without an intermediary device.
| Cable Type | End A | End B | Typical Use Case |
|---|---|---|---|
| Straight-Through | T568B | T568B | PC to switch, router to switch |
| Straight-Through | T568A | T568A | PC to switch (less common) |
| Crossover | T568A | T568B | PC to PC, switch to switch (legacy) |
RJ45 Pinout and Power over Ethernet (PoE): What Engineers Need to Know
The RJ45 pinout plays a critical role in Power over Ethernet (PoE) applications. PoE delivers DC power over the same Ethernet cable that carries data, and it uses specific pin pairs depending on the PoE mode:
| PoE Standard | Power Rating | PoE Mode | Pins Used for Power |
|---|---|---|---|
| IEEE 802.3af | 15.4W | Mode A (phantom power) | Pins 1-2, 3-6 (same as data) |
| IEEE 802.3af | 15.4W | Mode B (spare pairs) | Pins 4-5, 7-8 |
| IEEE 802.3at (PoE+) | 30W | Mode A or Mode B | Same pin assignments as af |
| IEEE 802.3bt Type 3 | 60W | Mode A or Mode B | Pins 1-2, 3-6 and/or 4-5, 7-8 |
| IEEE 802.3bt Type 4 | 90W | Mode A or Mode B | All 4 pairs (4-pair PoE) |
For PCB designers, the RJ45 connector selected must be rated for the intended PoE standard. Connectors carrying PoE must handle higher current per contact (up to 960mA for 802.3bt Type 4), which affects contact plating thickness, PCB trace width, and thermal management. For detailed PoE connector selection guidance, see our PoE RJ45 connector guide covering current ratings, thermal considerations, and connector selection criteria.
RJ45 Wiring Diagram and Signal Integrity at Higher Speeds
At Gigabit Ethernet (1000BASE-T) and above, the RJ45 pinout becomes more than just wire color matching — it directly impacts signal integrity. At these speeds, all four twisted pairs are used bidirectionally, and maintaining pair twisting as close to the connector as possible is critical. For a deeper dive into the magnetics that make this possible, see our LAN transformer guide.
For 10GBASE-T (10 Gigabit Ethernet over copper), the pinout requirements are even more stringent:
- Pair untwist length inside the connector should not exceed 13mm (0.5 inch)
- Shielded RJ45 connectors with metal housings are strongly recommended for 10G applications
- PCB trace impedance should be controlled to 100 ohms differential
- Crosstalk performance must meet or exceed Category 6A specifications
For high-speed Ethernet connector selection guidance including 10G RJ45 options, refer to our RJ45 connector buying guide which covers shielding, magnetics integration, and speed rating considerations. If you are also weighing different connector form factors, our RJ45 vs RJ11 comparison covers the key differences.
Common RJ45 Pinout Mistakes and How to Avoid Them
Even experienced engineers and technicians make pinout errors. Here are the most common mistakes and their consequences:
| Mistake | Symptom | Solution |
|---|---|---|
| Mixing T568A and T568B on straight-through cable | No link or intermittent connectivity | Verify both ends use the same standard; use a cable tester |
| Splitting Pair 3 (pins 3 and 6 on different wire pairs) | Crosstalk, reduced speed, link errors | Ensure pins 3 and 6 use wires from the same twisted pair |
| Untwisting pairs too far from connector | Signal degradation at Gigabit speeds | Maintain twist to within 13mm of the termination point |
| Wrong PoE pin assignment in PCB layout | PoE device fails to power or connector overheats | Follow IEEE 802.3 pin assignments; verify current ratings |
| Using unshielded connector for 10G application | EMI interference, packet loss | Use shielded RJ45 with metal EMI housing for 10GBASE-T |