Network Cable Length Loss Calculator

Why Ethernet cables have a speed limit

Every Ethernet cable is a compromise between signal strength and distance. As electrical pulses travel down copper pairs, they lose energy — a phenomenon engineers call attenuation — and the pairs interfere with each other, which is known as crosstalk. The longer the run, the weaker and noisier the signal arriving at the far end. Beyond a certain point the receiving equipment can no longer decode the bits reliably, and the negotiated speed drops.

That is why the networking world lives by the 100-meter rule: a full gigabit (1 Gbps) connection is rated for runs of up to 100 meters, including patch cords on both ends. The cable's category determines how well it holds up at higher frequencies. Cat5e is certified for gigabit at 100 meters but was never rated for 10-gigabit speeds. Cat6 can carry 10 Gbps, but only on shorter runs — roughly 55 meters. Cat6a, with its thicker shielding and tighter pair separation, sustains 10 Gbps for the full 100 meters.

How this calculator works

This calculator asks for three things: your cable category, the length of the run in meters, and the speed you need. It then applies an honest, simplified rule that mirrors the real standards. Up to each category's rated 10-gigabit distance — 55 meters for Cat6, 100 meters for Cat6a, and never for Cat5e — it reports a maximum real-world speed of 10 Gbps. From there up to 100 meters it reports 1 Gbps, from 100 to 150 meters 100 Mbps, and beyond that, down to about 10 Mbps, because very long runs eventually fall back to the slowest legacy rates.

Finally, it compares that achievable speed with the speed you said you need. If the cable comfortably covers your requirement, you get a clean bill of health. If it falls short, you get a clear bottleneck warning or a "too long" verdict with practical next steps.

Worked example

Imagine you are wiring a home office 90 meters of cable path away from the router, and you want a 10-gigabit link for video editing off a NAS. Select Cat6a: the calculator checks the rated distance — 100 meters for Cat6a — and since 90 is within it, it reports a maximum real-world speed of 10 Gbps and tells you the cable is not your bottleneck.

Now run the same 90 meters with plain Cat5e. Cat5e was never rated for 10 gigabits, so the calculator tops out at 1 Gbps for this run and flags a bottleneck: your cable cannot deliver the 10 Gbps you need. The fix is not a better router — it is a better cable (Cat6a) or a shorter run.

Practical tips

If you are pulling cable through walls today, buy Cat6a even if you only need a gigabit — the price difference is small and you will thank yourself in five years. For in-wall runs use solid-core cable, which performs better over distance than the stranded patch cords sold for desks. Keep Ethernet runs away from power lines and fluorescent ballasts to limit interference. If a run is already too long, a cheap $20 network switch placed roughly halfway regenerates the signal far more cheaply than replacing a 200-meter cable. And when you finish, test the run with a tool like iperf between two computers rather than trusting the green link LED — the LED only confirms a connection, not its speed.