Ethernet Trace Calculator
10/100 Mbps | Gigabit | 10 Gigabit Ethernet
Calculate trace width and differential impedance for Ethernet designs. From 10BASE-T to 10GBASE-T, get the right 100Ω differential pair dimensions for reliable network connectivity.
Ethernet Impedance Requirements
| Standard | Speed | Pairs Used | Differential Z |
|---|---|---|---|
| 10BASE-T | 10 Mbps | 2 pairs | 100Ω ±15% |
| 100BASE-TX | 100 Mbps | 2 pairs | 100Ω ±15% |
| 1000BASE-T | 1 Gbps | 4 pairs | 100Ω ±10% |
| 10GBASE-T | 10 Gbps | 4 pairs | 100Ω ±5% |
Ethernet PCB Design Guidelines
100Ω Differential
Ethernet requires 100Ω differential impedance. The tolerance varies by speed: ±15% for 10/100, ±10% for Gigabit, and ±5% for 10 Gigabit.
Transformer Coupling
Ethernet uses magnetics (transformers) for isolation. Maintain 100Ω impedance from PHY to transformer, and from transformer to RJ45 connector.
Length Matching
Keep differential pair traces within 5 mils of each other. For Gigabit+, match all 4 pairs to within reasonable tolerance (typically 100-200 mils).
Ethernet Layout Best Practices
PHY to Transformer
Transformer to RJ45
Speed-Specific Considerations
10/100 Ethernet
- • Relatively forgiving on impedance (±15%)
- • Uses only 2 of 4 pairs
- • Standard FR4 is fine
- • Less critical length matching
- • Common in cost-sensitive designs
Gigabit & 10G Ethernet
- • Tighter impedance tolerance needed
- • All 4 pairs are used bidirectionally
- • Better ground plane continuity required
- • More critical length matching
- • Consider low-loss PCB for 10G
Definitions and References
Ethernet is a packet-based local area networking technology used in industrial, commercial, and embedded systems. A cable assembly refers to terminated network or I/O cabling prepared for a specific interconnect job, while a wire harness is an organized bundle of conductors used to route signals or power through equipment and vehicles.
Calculate Your Ethernet Trace Dimensions
Use our free impedance calculator to determine exact trace width and spacing for your Ethernet design. Enter your stackup parameters for accurate 100Ω differential calculations.
Ethernet Design FAQ
What impedance does Ethernet use on a PCB?
Ethernet channels are usually designed around 100 ohm differential impedance, with tolerance tightening as data rate increases.
Do I need magnetics for Ethernet?
Yes. Isolation magnetics are standard between the PHY and the cable interface to provide common-mode rejection and safety isolation.
How short should Ethernet traces be?
Keep PHY-to-transformer routing short and direct, then keep the transformer-to-RJ45 section even shorter if possible.
Can I use integrated magnetics?
Yes. Many RJ45 connectors include integrated magnetics, which can simplify placement and routing when the layout still preserves pair symmetry.
What matters besides width?
Pair spacing, reference plane continuity, return path quality, and connector transitions all affect Ethernet signal quality in addition to width.
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