Ethernet Cable & PoE Calculator
Planning a cable run for a camera, access point or office? Check it will carry the speed you need, that your PoE device gets enough voltage at the far end, how much power the cable wastes, and the longest run that still works.
- Cat5 to Cat8
- PoE, PoE+ and PoE++
- Works in your browser
Will it work?
The numbers
Every speed on this cable
| Speed | Standard | Rated length on this cable | At your length |
|---|
Advice for this run
Maximum channel length by category
Lengths are for a full channel including patch leads, at 20 °C. "Usually" means it works in most installations but isn't guaranteed by the standards, so test it.
| Category | 1 Gbps | 2.5 Gbps | 5 Gbps | 10 Gbps | 25/40 Gbps |
|---|---|---|---|---|---|
| Cat5 | Usually 100 m | No | No | No | No |
| Cat5e | 100 m | 100 m | Usually 100 m | No | No |
| Cat6 | 100 m | 100 m | 100 m | 37 m (usually 55 m) | No |
| Cat6A | 100 m | 100 m | 100 m | 100 m | No |
| Cat7 / Cat7A | 100 m | 100 m | 100 m | 100 m | No |
| Cat8 | 30 m (usually 100 m) | 30 m (usually 100 m) | 30 m (usually 100 m) | 30 m (usually 100 m) | 30 m |
How it works it out
- Speed: each Ethernet standard (IEEE 802.3) is rated for a cable category and a channel length, normally 100 m: up to 90 m of fixed cable plus 10 m of patch leads.
- Patch leads are stranded and lose more signal per metre, so they count as 1.2 m (standard), 1.5 m (26 AWG) or about 2 m (28 AWG slim) for every metre, as in the TIA-568 cabling standard.
- Heat also increases signal loss: unshielded cable loses about 0.4% more per °C above 20 °C (0.6% above 40 °C), so hot runs must be shorter. Shielded cable loses about half that.
- PoE: we work out the exact current the device needs from its power and the cable's resistance (wire thickness, length, temperature and whether 2 or 4 pairs carry power), then check the voltage at the device, the current per pair and the switch's power budget against IEEE 802.3af, at and bt.
Things that catch people out
- CCA cable (copper-clad aluminium) is sold cheaply as "Cat6". It isn't standards-compliant, has about 55% more resistance, snaps easily, and can overheat at connections with PoE. Check for "solid copper" or "bare copper".
- "Cat7" with RJ45 plugs isn't a real Cat7 system: Cat7 needs GG45 or TERA connectors. With RJ45 it performs like Cat6A.
- There's no 50, 80 or 100 Gbps over copper twisted pair. Beyond 40 Gbps (and for 40 Gbps over 30 m) you need fibre or direct-attach cables.
- Over 100 m use a switch in the middle, a PoE extender, or fibre. Some switches have a long-reach mode that runs 10 Mbps up to about 250 m.
Does PoE slow down the network?
No. Power travels on the same pairs as data without interfering with it. The only indirect effect is heat: lots of high-power PoE cables bundled tightly together warm up, which increases signal loss, so very hot bundles should be shorter or use Cat6A.
Why does the switch's voltage matter?
The higher the starting voltage, the less current the device needs for the same power, so less is lost in the cable. Most switches output 50 to 54 V. The standards guarantee a device works on a compliant 100 m run even at the lowest allowed voltage (44 V for PoE, 50 V for PoE+ and Type 3, 52 V for Type 4).
What's the difference between PoE classes and the device's real power?
The switch reserves power by class (for example 30 W for a Class 4 PoE+ device), but the device may draw less. This calculator uses the power you enter, so enter the device's maximum (for example with heaters, IR lights or all radios on).
Can I run 10 Gbps over my existing Cat6?
Often yes on shorter runs. The standards support up to 55 m on Cat6, but only 37 m is safe where many cables run together (alien crosstalk). Certify the link with a cable tester, or use Cat6A for new 10 Gbps runs and for Wi-Fi 7 access points.