How Far Can You Run Ethernet Cable?

The short answer is 100 metres, or 328 feet. The useful answer is more nuanced, because that number is a total budget, not the length of the cable you pull through the wall, and several everyday conditions quietly shrink it. Whether you're wiring a house, running a camera to the far corner of a warehouse, or pulling cable through conduit to an outbuilding, understanding where the limit comes from tells you exactly when you can stretch it and when you need a different approach entirely.

The Real Rule: 90 Metres Plus 10

The 100-metre figure comes from the ANSI/TIA-568 and ISO/IEC 11801 cabling standards, and it's echoed in IEEE 802.3 for every BASE-T Ethernet variant. But the standard doesn't describe one long cable. It describes a channel, the complete path from switch port to device, and it splits that channel in two.

• 90 metres (295 ft) of permanent link: the solid-core cable installed in walls, ceilings, and conduit.
• 10 metres (33 ft) of patch cords: the flexible stranded cables at both ends combined, one from the patch panel to the switch, one from the wall jack to the device.

This matters more than most people realise. If you run 98 metres in the wall and then plug in two 3-metre patch cords, you're over budget even though the in-wall run looked fine. Stranded patch cable also attenuates the signal more than solid cable does, which is why the standard rations it so carefully. Keep patch cords short.

Distance by Category and Speed

Here's a myth worth killing early: a higher category does not buy you more distance. Cat5e, Cat6, and Cat6a all stop at 100 metres. What changes with category is the speed you can sustain over that distance.

The Cat6 line is the one that catches people out. It handles gigabit across the full 100 metres, but push it to 10 Gbps and it's only good for roughly 55 metres, less still in a noisy environment with alien crosstalk. If you're wiring for 10G, Cat6a is the honest choice. Our guide on how to choose Ethernet cable covers the category trade-offs in full.

Why 100 Metres, Exactly?

It's physics, not an arbitrary rule. As a signal travels down copper it weakens (attenuation, or insertion loss), it bleeds into neighbouring pairs (crosstalk), some of it reflects back (return loss), and the four pairs arrive at slightly different times (delay skew). The standard adds up the worst case for all of these and finds that at 100 metres the loss budget is spent. Beyond that, the receiver can no longer reliably reconstruct what was sent.

What Actually Shrinks Your 100 Metres

This is where theory meets a real building, and where several installs quietly fall short of spec.

Heat

Copper's resistance rises with temperature, which increases attenuation, which shortens your usable run. The effect is significant: a Cat6 permanent link rated for about 295 feet at a comfortable 68°F (20°C) should be held to roughly 250 feet at 122°F (50°C). If your cable runs through an attic, a hot industrial space, a rooftop conduit, or anywhere in direct sun, apply temperature derating and plan shorter runs. This is the single most overlooked factor in real-world cabling.

Workmanship

Kinked cable, a bend tighter than the minimum radius, over-tightened cable ties that crush the jacket, and untwisted pairs at the termination all raise resistance and delay skew, eating into your margin. Support cable properly with the right straps and supports, maintain the pair twist right up to the connector, and never staple through a run.

Cheap cable

Copper-clad aluminium (CCA) cable has noticeably higher resistance than solid bare copper. It attenuates faster, performs worse over distance, and is particularly bad for Power over Ethernet, where the extra resistance produces heat and voltage drop. Buy solid bare copper for anything permanent.

Shielding won't help

Another myth: shielded cable does not extend your maximum distance. Shielding fights electromagnetic interference, which is valuable in noisy environments, but the 100-metre limit stands regardless. Poorly grounded shielding can actually make things worse.

What Happens If You Go Over?

The cable does not stop working at 328 feet and one inch. That's the trap. A 110- or even 120-metre run will often link up and appear to work, especially under light load, which convinces people the limit is soft. What you've actually done is spend your entire safety margin.

The symptoms show up later: intermittent packet loss, throughput that collapses under heavy load, a switch that quietly negotiates down from 1 Gbps to 100 Mbps to stay stable, and the classic signature of an overlong run, a link that works perfectly all winter and starts dropping in summer when the cable heats up and copper resistance rises. For a home lab, that risk may be acceptable. For anything you depend on, it isn't.

How to Go Farther Than 100 Metres

If the distance genuinely exceeds the limit, there are proper solutions. Pick based on speed, power, and how much you care about reliability.

The standards-compliant approach in a commercial building is to add a telecommunications room or an intermediate switch so that every channel stays inside its 100-metre budget. The cheapest approach, an extender on the existing copper, works but sits outside TIA-568 and puts a powered device out in the field where it's harder to manage. For a mid-run switch or extender in a garage, warehouse, or outdoor location, house it in a proper NEMA enclosure rather than leaving it exposed.

Between Buildings, Use Fiber

This is a safety point, not just a performance one. Copper running between separate structures creates a conductive path between two different grounding systems. A difference in ground potential, or a nearby lightning strike, can send damaging or dangerous energy straight down that cable and into your equipment. Fiber is dielectric: it carries no current, so it breaks that path entirely, while also shrugging off electrical interference and covering far greater distances. If copper between buildings is unavoidable, it needs proper surge protection and grounding at both ends. Fiber is simply the better answer.

A Note on Power over Ethernet

PoE is bound by the same 100-metre limit, and distance affects it in an additional way: voltage drops over length, so a device at the far end of a long run receives less power than one nearby. Thin or CCA conductors make this worse. If a camera, access point, or PoE light sits beyond 100 metres, a PoE extender can carry both data and power farther, which is why they're common for surveillance cameras, call boxes, access control panels, and PoE lighting in large facilities.

Practical Planning Checklist

• Budget the whole channel, not just the in-wall run: 90 m permanent link plus 10 m of patch cords.
• Measure the real cable path, not the straight-line distance. Cable goes up, across, and back down.
• Derate for heat in attics, roofs, and industrial spaces.
• Use solid bare copper for permanent runs, stranded only for short patch cords.
• Certify the link after installation rather than assuming it passes.
• Go fiber for anything long, between buildings, or in heavy electrical noise.

The Bottom Line

Ethernet's 100-metre limit is a total channel budget, split 90 metres of in-wall cable plus 10 metres of patch cords, and it's set by the physics of signal loss rather than by convention. Heat, poor workmanship, and cheap copper-clad cable all shave metres off that figure before you've even started, and a higher cable category buys you speed, not reach. Exceeding the limit rarely fails outright, which is exactly what makes it dangerous: it fails later, intermittently, and usually in summer. Plan the whole channel, derate for temperature, and when the distance genuinely calls for it, add a switch or run fiber rather than hoping copper will stretch.