Check TIA-568 channel insertion loss for a copper twisted-pair run, see pass/marginal/fail margin, find the fastest Ethernet standard your cable category and length actually support — and look up T568A/T568B wiring, color codes, and crossover cables.
A standard channel is a 100m link: up to 90m of permanent-link (solid) cable plus up to 10m total of stranded patch cords at each end, through up to 4 connections.
Insertion loss is the reduction in signal strength (in dB) as a signal travels through a cabling channel — the cable itself, plus every connector and patch cord along the way. TIA-568-C.2 defines a maximum allowable insertion loss for each cable category at a 100-meter channel length, tested at that category's rated frequency.
Too much insertion loss means the receiving equipment can't reliably recover the signal, causing packet loss, retransmissions, or link speed downshifts (e.g. a 10GBASE-T port falling back to 1G).
| Category | Test freq. | Max loss (100m channel) |
|---|---|---|
| Cat5e | 100 MHz | 24.0 dB |
| Cat6 | 250 MHz | 21.3 dB |
| Cat6A | 500 MHz | 20.9 dB |
Reference values — confirm against the current published TIA-568-C.2/D standard for certification work.
It doesn't — higher category cable is actually rated to higher frequencies (Cat6A up to 500 MHz vs. Cat5e's 100 MHz) because better shielding, tighter twist rates, and improved dielectric materials let it carry more bandwidth before loss becomes a problem. The max allowed loss numbers above look similar across categories because each category is tested at a different, harder frequency — a fair comparison would ask "how much loss at the same frequency," where better cable always wins.
Say you've got a 75m Cat6 permanent link run from an IDF to a desk, and someone wants to plug in a 10GBASE-T switch port at both ends. Two separate checks matter here, and it's easy to only run one of them:
Check 1 — insertion loss. Cat6's TIA-568-C.2 limit is 21.3 dB over a 100m channel at 250 MHz. Scaled to 75m, the budget is roughly 21.3 × (75/100) = 16.0 dB, and a well-installed 75m Cat6 run should land close to that estimate. On pure attenuation, this run is fine — there's no reason a 10GBASE-T signal can't physically travel 75m of Cat6 without excessive loss.
Check 2 — the real limiter. 10GBASE-T over Cat6 isn't actually loss-limited in most real installs; it's limited by alien crosstalk from adjacent cables in the same bundle, which is a separate spec (ANEXT/AXT) this calculator's insertion-loss numbers don't cover. IEEE 802.3an guarantees only 37m worst-case for unshielded Cat6 in a bundled, high-density run — up to about 55m in a lighter-density or shielded install. A 75m Cat6 run is past even the optimistic end of that range, so it's a real risk for 10G even though the raw insertion-loss math looks comfortable. The fix, if 10G is required, is either Cat6A cable for that run or accepting the link may negotiate down to 1G or 2.5GBASE-T instead (both of which are solidly within spec at 75m on Cat6).
This is the single most common mistake installers make with this kind of math: insertion loss passing doesn't mean a higher-speed standard is supported — check the category/speed/distance table on the "Max speed by category" tab too.
Does a shorter cable always mean lower loss?
Yes for a fixed frequency and cable type — insertion loss scales roughly linearly with length. But going from Cat6 to Cat6A at the same length lowers loss more than shortening a Cat6 run by a few meters would, because Cat6A's tighter twist rates and thicker conductors reduce loss-per-meter at any given frequency.
My cable tester reports a different number than this calculator — which one is right?
Trust the tester. This calculator scales the TIA-568-C.2 standard's maximum-allowed loss linearly by length as a field estimate; a certified tester measures your actual installed cable, connectors, and terminations, which is always the authoritative number for certification or troubleshooting a specific run.
Why does the "connections in channel" field not change the result?
The TIA-568-C.2 channel limit already assumes up to 4 connections (2 permanent-link ends plus 2 patch cord ends) as part of the standard 100m channel definition — it's shown here for reference since exceeding 4 connections is itself an out-of-spec condition worth flagging, not because each connector's individual loss is broken out in this version of the tool.
Can I use this for a permanent link test instead of a full channel?
The 90m permanent-link limit is roughly 0.9× the 100m channel limit shown here (TIA-568-C.2 defines it as a slightly tighter per-meter budget since it excludes patch cords) — close enough for field estimation, but use the channel numbers above if you're testing with patch cords attached at both ends, which is the more common real-world test configuration.