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Cable Length Limit Calculator

Work out cable length limit instantly with clear inputs, formula shown and shareable results.

About Cable Length Limit Calculator

The 100 m Ethernet channel limit includes patch cords at both ends, so the permanent link in the wall is typically capped at 90 m. Copper derates further in heat — roughly 0.4 percent per degree above 20 C — and in dense bundles where mutual heating raises the conductor temperature, which is why PoE-heavy installations need shorter runs.

Formula

Length limit

derated channel = standard limit x (1 - temperature derating - bundle derating); permanent link = derated - patch cord length

Worked example

With the default values below, Cable Length Limit Calculator returns Permanent link length available of 84.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Cable and standardone of Cat 5e - 1000BASE-T, Cat 6 - 10GBASE-T, Cat 6a - 10GBASE-T, OM4 multimode - 10G, OM4 multimode - 100G SR4
Cat 6a - 10GBASE-T
Patch cords at both endsminimum 0 m
10 m
Ambient temperatureaccepts -10–70 C
35 C
Cables in the bundleminimum 1
24

Results

Permanent link length available
84.0 m
Standard channel limit
100 m
Derating applied
6.00%
Derating note
Copper derates with temperature and bundle density; fibre does not

Step by step

  1. 1Values used
  2. 2Length limit
  3. 3Permanent link length available= 84.0 m
  4. 4Standard channel limit= 100 m
  5. 5Derating applied= 6.00
  6. 6Derating note= Copper derates with temperature and bundle density; fibre does not

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is Cat 6 limited to 55 m for 10GBASE-T?

Alien crosstalk between adjacent cables. Cat 6a adds tighter twisting and often shielding to control it, restoring the full 100 m.

Does PoE affect the length limit?

Indirectly. Power dissipation heats the conductors, and the resulting temperature rise derates the permitted length, which matters most for high-power PoE in full bundles.

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