Ethernet Cable Length Calculator
Calculate how much ethernet cable you need including routing overhead for walls, ceilings, and slack.
Avoid buying too little or too much.
How Ethernet Cable Length Limits Are Calculated
Ethernet has strict maximum cable length limits due to signal attenuation and propagation delay. Exceeding these limits causes packet loss, retransmissions, and reduced throughput.
Maximum Cable Lengths by Standard:
| Standard | Speed | Max Length |
|---|---|---|
| Cat5e (1000BASE-T) | 1 Gbps | 100 meters |
| Cat6 (1000BASE-T) | 1 Gbps | 100 meters |
| Cat6A (10GBASE-T) | 10 Gbps | 100 meters |
| Cat8 (40GBASE-T) | 40 Gbps | 30 meters |
The 100-meter limit for standard Ethernet is defined by IEEE 802.3:
Max Segment = 90m (structured cabling) + 10m (patch cables)
Signal Attenuation Reference: Cat5e at 100 MHz: max attenuation of 24 dB over 100 meters. Beyond 100m, noise overwhelms signal.
Worked Example: Running cable from router (basement) to office (2nd floor):
- Vertical run: 5m
- Horizontal ceiling run: 35m
- Patch cables each end: 2m + 2m
- Total: 44 meters — well within 100m limit
Extending Beyond 100 Meters:
- Network switch: regenerates signal, resets 100m limit
- Media converter + fiber: fiber runs up to 2 km (single-mode) or 550m (multi-mode)
- PoE (Power over Ethernet): same 100m limit applies — voltage drop is additional concern
Testing Tools: A cable tester or TDR (time-domain reflectometer) measures actual cable length and detects faults.