What is the maximum length for a Cat6 cable?

100 meters at 1 Gigabit, the same as Cat5e. At 10 Gigabit, TIA TSB-155-A rates 10GBASE-T over Cat6 at 37 meters in the worst alien-crosstalk case and up to 55 meters once crosstalk is mitigated. If the run is longer than 37 meters and the link has to be 10 Gigabit, use Cat6a, which is rated for the full 100 meters.

OM3 vs OM4: how much further does OM4 go?

At 10 Gigabit (10GBASE-SR) OM3 reaches 300 meters and OM4 reaches 400 meters. At 40 Gigabit (40GBASE-SR4) it is 100 versus 150 meters. At 25 and 100 Gigabit (25GBASE-SR, 100GBASE-SR4) it is 70 versus 100 meters. OM4 buys roughly a third more distance on the same duplex or parallel optics; past those numbers the answer is OS2 single-mode, not a better multimode grade.

How long can a DAC or AOC cable be?

Passive direct-attach copper is short by design: up to 7 meters for 10 Gigabit SFP+ assemblies, 5 meters for 25GBASE-CR, 7 meters for 40GBASE-CR4 and 5 meters for 100GBASE-CR4. Active optical assemblies are vendor-specified rather than IEEE-rated and commonly run 1 to 30 meters, which is why they are the usual answer for a cross-aisle link that a DAC cannot make.

Does a longer cable make the connection slower?

Not within the rated length — an in-spec 90 meter run performs the same as a 3 meter one. Past the budget the link does not gracefully slow down: the receiver starts missing frames, retransmissions climb, and a 10GBASE-T link will often fail to train or drop to a lower speed instead. Fix the length, do not tune around it.

How should I measure the run before ordering?

Measure the path the cable actually takes — up the wall, along the tray, down to the port — not the straight-line distance across the room, and add a service loop at each end. Then keep 90 meters as the ceiling for the fixed horizontal run so the patch cords at both ends still fit inside the 100 meter channel.

Ethernet cable length limits & cable picker

How far each media type is rated to carry 1G through 100G — and the cables we stock at that length.

Link planner

Will it reach?

Enter the link speed and the length of the actual cable route — the path it takes through walls and trays, not the straight line. We show which media are rated to carry it, then filter the cables below to match.

Link speed

Cable run length

Cat6a copper carries 10 GbE over this run

Rated reaches at this speed — anything marked Works has published headroom for the run you entered.

Cat5e copper—Not rated
Cat6 copper37–55 mWorks
Cat6a copper100 m (328 ft)Works
DAC — passive twinaxup to 7 mToo far
AOC — active optical1–30 m typicalWorks
OM3 multimode fiber300 mWorks
OM4 multimode fiber400 mWorks
OS2 single-mode fiber10 kmWorks

Filters to cables at least as long as the run — add slack for the route and the service loop.

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Specifications are read from the manufacturer product title as supplied to us; where a value is not stated it is left blank rather than estimated. Every line is screened for TAA country-of-origin and NDAA §889 status before checkout.

Reference

Maximum cable length by media type and speed

The familiar 100 meter (328 foot) Ethernet limit is a channel budget rather than a property of the cable: ANSI/TIA-568 allows 90 meters of fixed horizontal cable plus up to 10 meters of patch cords across both ends. Every other figure below comes from the IEEE 802.3 clause that defines the physical layer in question — with the single exception of the AOC row, which is vendor-specified and footnoted as such — so the number changes with the speed you are running, not with the brand on the jacket.

Maximum supported cable run by media type and Ethernet speed, from the published IEEE 802.3 and TIA figures.
Cable / media	1 GbE	10 GbE	25 GbE	40 GbE	100 GbE
Cat5e copper	100 m (328 ft)	—	—	—	—
Cat6 copper	100 m (328 ft)	37–55 m	—	—	—
Cat6a copper	100 m (328 ft)	100 m (328 ft)	—	—	—
DAC — passive twinax	—	up to 7 m	up to 5 m	up to 7 m	up to 5 m
AOC — active optical	—	1–30 m typical	1–30 m typical	1–30 m typical	1–30 m typical
OM3 multimode fiber	550 m	300 m	70 m	100 m	70 m
OM4 multimode fiber	550 m	400 m	100 m	150 m	100 m
OS2 single-mode fiber	5 km	10 km	10 km	10 km	10 km

Cat6 at 10 Gigabit: TIA TSB-155-A gives 37 meters in the worst alien-crosstalk case and up to 55 meters once crosstalk is mitigated. Treat anything past 37 meters as a link that needs a survey, or specify Cat6a.
AOC is the one row above that is not an IEEE figure: active optical assemblies are vendor-specified, and real 10G through 100G parts range from about 1 to 30 meters depending on the maker. The 1–30 m shown is typical rather than rated — check the reach on the specific part before you commit a run to it.
100 Gigabit multimode: the table uses today's 100GBASE-SR4 QSFP28 figures (70 m on OM3, 100 m on OM4). The older 100GBASE-SR10 parallel optics reached 100 m and 150 m, which is what most third-party tables still print.
2.5GBASE-T and 5GBASE-T (IEEE 802.3bz) run the full 100 meters on existing Cat5e and Cat6 — the reason a building does not need re-cabling to get past 1 Gigabit.
25GBASE-T and 40GBASE-T over Cat8 reach 30 meters on a two-connector channel. That is a top-of-rack option rather than a building cable; we quote it on request.
Power over Ethernet does not change the length limit — 100 meters still applies. What changes with length is voltage drop, which is why an 802.3bt source budgets more power than the device at the far end receives.

Media choice

When fiber beats copper

Distance is the obvious trigger, and it is not the only one. Four conditions push a link to fiber regardless of length, and one keeps it on copper no matter how attractive the optics look.

The run is past the 100 meter channel

Copper stops at the TIA budget and there is no compliant way to extend it. A 150 meter run is an OM4 or OS2 run, even at 1 Gigabit.

The link leaves the building or the power domain

Fiber is a dielectric: it carries no current between structures, so there is no bonding requirement, no ground-potential difference across the pair, and no metallic path for a nearby strike to follow into the switch.

The route is electrically noisy

Motor rooms, elevator shafts, generator plants and industrial floors put copper next to sources that raise the bit error rate. Fiber is immune to that noise, which is often worth more than the distance.

The speed is above 10 Gigabit outside a rack

25, 40 and 100 Gigabit over twisted pair means Cat8 at 30 meters. Anything longer than a rack row is OM4 for the aisle or OS2 for the campus.

Where copper still wins

Powered endpoints (fiber carries no power), 1 and 10 Gigabit drops inside the 100 meter budget, and cost per port. In-rack, a passive DAC beats optics on both price and power draw for the first few meters.

FAQ

Cable length questions

What is the maximum length of an Ethernet cable?: 100 meters (328 feet) for Cat5e, Cat6 and Cat6a running 1 Gigabit Ethernet. That figure is a channel budget, not a cable rating: ANSI/TIA-568 allows 90 meters of fixed horizontal cable plus up to 10 meters of patch cords across both ends. 10GBASE-T holds the same 100 meters only on Cat6a — on Cat6 it is 37 to 55 meters.
What is the maximum length for a Cat6 cable?: 100 meters at 1 Gigabit, the same as Cat5e. At 10 Gigabit, TIA TSB-155-A rates 10GBASE-T over Cat6 at 37 meters in the worst alien-crosstalk case and up to 55 meters once crosstalk is mitigated. If the run is longer than 37 meters and the link has to be 10 Gigabit, use Cat6a, which is rated for the full 100 meters.
OM3 vs OM4: how much further does OM4 go?: At 10 Gigabit (10GBASE-SR) OM3 reaches 300 meters and OM4 reaches 400 meters. At 40 Gigabit (40GBASE-SR4) it is 100 versus 150 meters. At 25 and 100 Gigabit (25GBASE-SR, 100GBASE-SR4) it is 70 versus 100 meters. OM4 buys roughly a third more distance on the same duplex or parallel optics; past those numbers the answer is OS2 single-mode, not a better multimode grade.
How long can a DAC or AOC cable be?: Passive direct-attach copper is short by design: up to 7 meters for 10 Gigabit SFP+ assemblies, 5 meters for 25GBASE-CR, 7 meters for 40GBASE-CR4 and 5 meters for 100GBASE-CR4. Active optical assemblies are vendor-specified rather than IEEE-rated and commonly run 1 to 30 meters, which is why they are the usual answer for a cross-aisle link that a DAC cannot make.
Does a longer cable make the connection slower?: Not within the rated length — an in-spec 90 meter run performs the same as a 3 meter one. Past the budget the link does not gracefully slow down: the receiver starts missing frames, retransmissions climb, and a 10GBASE-T link will often fail to train or drop to a lower speed instead. Fix the length, do not tune around it.
How should I measure the run before ordering?: Measure the path the cable actually takes — up the wall, along the tray, down to the port — not the straight-line distance across the room, and add a service loop at each end. Then keep 90 meters as the ceiling for the fixed horizontal run so the patch cords at both ends still fit inside the 100 meter channel.

Need help sizing it?

Send the run lengths, the switch ports at each end and the count — we come back with media, connectors and a total, screened for TAA country-of-origin and NDAA §889 status before checkout.

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