Cable Speed Calculator
The formula
What the copper link speed tells you
What the cable plant actually negotiates at its length: category reach limits turning a “10-gig” cable into a 1-gig link at 80 meters.
Calculation: Rated speed capped by length per category; cost per Gbps = drops × cost ÷ aggregate. Enter your inputs and every substitution is shown below the result.
Reading the result
If the run is beyond the category limit, the link falls back silently — the speed you pay for is the speed the PHY shakes hands at.
Rules of thumb: New installs default Cat6A: 10 Gb full 100 m and PoE++ headroom.
Limitations and best practice
The limit is per-continuous-run; a patch panel, a bad crimp and two “gigabit” switches in series will surprise you later.
This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Frequently asked questions
Is Cat8 worth it?
Why does my gig link run 700 Mbps?
Source & methodology
TIA-568 category specifications; IEEE 802.3 10GBASE-T reach rules.
Cable Speed explained: formula, worked example and honest limits
You are here because you need a specific number, and you want to see how it was produced before you rely on it. Cable Speed is the kind of number people argue about from memory. This page ends that argument with arithmetic you can watch happen: enter your figures, get Negotiated link speed in real time, and see every substitution printed below.
It helps to separate the mechanics from the interpretation. The mechanics are fixed: Rated speed capped by length per category; cost per Gbps = drops × cost ÷ aggregate. Anyone, anywhere, entering the same inputs will get the same 10.0 Gb/s. The interpretation is where experience counts: whether 10.0 Gb/s is good, normal or alarming depends on comparisons covered below, and that is the part most articles about Cable Speed never explain.
What makes Cable Speed worth calculating is not precision but position: it tells you which side of a threshold you are on, and by how much. A rough figure that settles the direction beats an elaborate one that never commits.
Every figure in the prose is generated by the engine rather than written beside it — the worked example resolves to negotiated link speed = 10.0 Gb/s on the default inputs. Read the sections in order and you will be able to reproduce every figure by hand.
Every input in Cable Speed, and what it does to the answer
One formula, published in full: Rated speed capped by length per category; cost per Gbps = drops × cost ÷ aggregate. Anything you can read, you can reproduce in a spreadsheet, and that reproducibility is the whole point of printing it rather than hiding it behind a button.
Cable category (example value Cat6 (10 Gb ≤55 m)) is a categorical input — the option you choose decides which numbers the formula uses. Replace the example with the figure from your own records — the tool recomputes instantly and the printed steps follow your numbers.
Run length (meters) (example value 36) is a numeric input whose unit is fixed by the label; a wrong unit is a wrong answer wearing a plausible disguise. Keep every length field in the same unit; the formula assumes a consistency it cannot check for you.
Number of runs (example value 1) is a plain measured quantity — the unit shown in the label is the unit the formula expects. Count from the record, not the estimate; whole-number inputs are cheap to verify and expensive to get wrong.
Cost per drop installed ($) (example value 185) is a numeric input whose unit is fixed by the label; a wrong unit is a wrong answer wearing a plausible disguise. Keep every money input in the same currency; mixing systems quietly corrupts the comparison.
What each “Cable category” choice actually does: Cat5e (1 Gb/s) → 1.0 Gb/s · Cat6 (10 Gb ≤55 m) → 10.0 Gb/s · Cat6A (10 Gb) → 10.0 Gb/s · Cat7/8 (25/40 Gb ≤30 m) → 10.0 Gb/s These figures are computed from this engine, not estimated — switch the dropdown above and you will land on exactly these numbers.
Cable Speed with real numbers, step by step
Abstract formulas are hard to trust, so here is the complete substitution using the default inputs, written the way an examiner would want it. Starting figures: Cable category, Run length (meters), Number of runs, Cost per drop installed ($). The endpoint of that chain is 10.0 Gb/s of negotiated link speed, sitting in the “Full-rate plant” band.
- Category rated 10 Gb/s to 55 m
- 36 m within limit → 10 Gb/s per link
- 1 drops × 10 = 10 Gb/s aggregate
- Install cost 185 → 19 per Gb/s
Length limit for full rate — 55 m. Read next to the headline, this is the figure that shows the shape of the trade-off.
Cost per Gb/s of aggregate — $19. If your inputs change, this is usually the first companion figure to move.
Aggregate capacity across drops — 10.0 Gb/s. Read next to the headline, this is the figure that shows the shape of the trade-off.
Headroom vs 100 m standard — 64 m. Compare it against the main result of 10.0 Gb/s before drawing conclusions.
Keep this worked example open while you enter your own figures: matching the shape of the substitution is the fastest way to spot a unit or convention mistake.
Reading the result: bands, zones and thresholds
Nobody acts on a bare figure — they act on a figure with a comparison attached. On the example inputs the band reads “Full-rate plant”; your own figures place you on a different rung of the same ladder. The practical reading rules: compare against your own history before comparing against other people; treat band boundaries as zones, not walls — one point on the wrong side of a threshold rarely changes a real outcome; and when a companion output contradicts the headline, believe the pair.
Placing this figure in context: calculators of this kind differ less in arithmetic than in what they choose to ignore. This one keeps Cable category explicit so that the omissions are visible rather than hidden in a preset.
The errors that quietly break a Cable Speed figure
The limit is per-continuous-run; a patch panel, a bad crimp and two “gigabit” switches in series will surprise you later. This calculator gives an estimate based on standard formulas; it is not professional financial, medical, legal or engineering advice. Verify anything you plan to act on with a qualified professional and your own records.
Comparing a Cable Speed computed here with a figure from another source that uses different conventions. Same name, different denominator — the disagreement is usually in the definitions, not the data.
Another is comparing across contexts: a Cable Speed computed with one set of conventions should never be lined up against a figure computed with another. Check the inputs behind both before ranking them.
A quick check for any Cable Speed figure
- Record the date and the inputs alongside the number so future-you knows what was assumed.
- Re-run the calculation with a ±10 % stress on the two most sensitive inputs.
- Confirm the inputs are dated — a Cable Speed figure should carry the date it was computed.
- Verify each input against its original source document, not memory.
- Note the date and the inputs beside the number so the figure can be audited later.
- Run the ±10 % stress on the top two levers and check that your conclusion survives both.
Step by step: getting a trustworthy Cable Speed out of this tool
The tool does the arithmetic; the routine below is what makes the arithmetic trustworthy. Five steps, a minute total — and afterwards you will know not just what the number is, but which assumption produced it.
Step 1 — start from evidence. The inputs behind Cable Speed are cable category, run length (meters), number of runs, cost per drop installed ($). Write them down with their source next to each one; if you cannot name where a figure came from, that is the input most likely to be wrong. A figure with a date beside it becomes evidence; without one it stays an anecdote.
Step 2 — compute the version you would not be embarrassed by. If a stranger audited your inputs, which set would you hand over? Enter that set, read the result, and treat everything else as upside. Estimates improve most when the worst case is written down in ink.
Step 3 — play with the inputs on purpose. Ten percent up, ten percent down, one field at a time. Within a few minutes you will know this calculation better than most people who quote its results. The test of a good estimate is not that it feels right but that it changes what you do.
Step 4 — compute a corridor, not a point. Three runs — worst, likely, best — turn Cable Speed from a snapshot into a range. Plan against the pessimistic end and treat the optimistic end as the upside story. The inputs are the part of the work that nobody else can do for you.
Step 5 — write the one-line memo. “Negotiated link speed = 10.0 Gb/s on this date, from these inputs.” That line is the entire deliverable; everything else on this page is how you earned the right to write it. The test of a good estimate is not that it feels right but that it changes what you do.
Who actually uses Cable Speed — and when
In Networks & Storage the figure computed here is usually the first one somebody asks to see. Having it — with the formula behind it — changes your position in the conversation from participant to reference. Write the figure down before moving on; memory flatters whichever number you saw last.
Used properly this is a five-minute filter that saves weeks. Compute Cable Speed, reject what fails, and only then bring in the expensive analysis for the survivors. Compare the calculation to the rough guess you arrived with, and ask why they differ.
Re-running this page costs nothing and catches the slow drifts that never announce themselves. In Technology & Computing the expensive mistakes are rarely sudden; they are small changes in Cable category that nobody recalculated for a year. Say the answer out loud before you save it; if it sounds wrong, the model did not change, your understanding did.
Cable Speed — frequently asked questions
How much does the “Cable category” choice change the answer?
The spread is not cosmetic: this choice alone takes Cable Speed from 1.0 Gb/s to 10.0 Gb/s with every other input frozen, which is more influence than most of the numeric fields on this page can claim.
What is a typical Cable Speed?
With the example inputs on this page the result is 10.0 Gb/s, labelled “Full-rate plant”. “Typical” varies with situation, which is why every result here ships with its verdict band and its sensitivity list: they turn one figure into a range you can locate yourself inside.
How do I calculate Cable Speed by hand?
Rated speed capped by length per category; cost per Gbps = drops × cost ÷ aggregate is the entire method. Work the inputs in that order — Category rated 10 Gb/s to 55 m — and you will reach 10.0 Gb/s on the default figures, the same number this tool prints.
Is the Cable Speed result of 10.0 Gb/s good or bad?
The tool answers “what”, not “whether”: 10.0 Gb/s carries the verdict “Full-rate plant” for the default case, which is a starting interpretation rather than a verdict on your situation. Re-run with your own figures and compare the bands.
Is Cable Speed accurate?
The arithmetic is exact: Rated speed capped by length per category; cost per Gbps = drops × cost ÷ aggregate is evaluated with full floating-point precision and every substitution is printed in the worked example. What limits accuracy is input quality and the model’s assumptions, so treat the 10.0 Gb/s result as the correct answer to the question you typed — and check the assumptions section before acting on it.
What affects Cable Speed the most?
Sensitivity depends on where you start, but the inputs Cable category and Run length (meters) typically move Cable Speed further than the rest because they enter the formula multiplicatively. If you can only measure two things well, measure those and hold the others at conservative defaults.
Is Cat8 worth it?
Only inside racks under 30 m; beyond that it is Cat6A money for Cat6A speed.
Why does my gig link run 700 Mbps?
That is TCP goodput with 1500-byte frames near the efficiency ceiling of this category math — see the ethernet-speed engine.
Can this tool see the numbers I type?
It cannot. There is no submission step: the calculation happens in your browser and the result disappears when you close the page. Treat the fields above as a scratchpad rather than a form.
What the labels on this page mean
- Length limit for full rate
- 55 m in the default Cable Speed calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- Cost per Gb/s of aggregate
- $19 for the Cable Speed worked case; it sits next to the main result because it carries context the headline leaves out.
- Aggregate capacity across drops
- 10.0 Gb/s in the default Cable Speed calculation — one of the secondary figures an experienced reader checks before trusting the primary number.
- Negotiated link speed
- The primary output of this tool: 10.0 Gb/s for the default inputs, computed exactly from Rated speed capped by length per category; cost per Gbps = drops × cost ÷ aggregate.
- Worked example
- The calculation written out in full so that nothing on this page has to be taken on trust.
- Verdict band
- The plain-language label — here “Full-rate plant” — mapping the computed figure onto experience-based ranges for Technology & Computing.
Where the Cable Speed model comes from
There is no black box on this page — the engine evaluates Rated speed capped by length per category; cost per Gbps = drops × cost ÷ aggregate. Source of record: TIA-568 category specifications; IEEE 802.3 10GBASE-T reach rules. Any other implementation of this model should return the same figure for the same inputs. If one does not, the difference is in its assumptions — which this page prints and that one probably does not.
This page is an estimation aid, not professional advice. The design rule is simple: two people entering identical figures must get identical answers. The promise to the reader is narrow and testable: same inputs, same output, no silent rounding, and no figure presented without the formula that produced it.
What to do with your Cable Speed next
Re-run the calculation with your own figures, stress the two most sensitive inputs by ±10 %, and only then act on the result.
The audience here is people who need one trustworthy number before their next decision. Everything you need to defend the result — formula, substitution, sensitivity, source — is printed above, so the only remaining variable is the honesty of your inputs.