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
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 for Ethernet?
All Ethernet standards use 100Ω differential impedance. The tolerance ranges from ±15% (10/100) to ±5% (10G).
Do I need magnetics for Ethernet?
Yes. Ethernet requires isolation transformers (magnetics) between the PHY and the RJ45 connector for safety and common-mode rejection.
How short should traces be?
PHY to transformer: 2-3 inches max. Transformer to RJ45: as short as possible, ideally under 1 inch.
Can I use integrated magnetics?
Yes! Many RJ45 jacks include built-in magnetics. This simplifies layout—just route 100Ω differential pairs from PHY to jack.
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