Documentation sections

Ethernet Cable Length & Attenuation Calculator

POSThttps://rftools.io/api/py/v1/calculate

Slug ethernet-cable. Calculate Ethernet cable attenuation, maximum cable length, and pass/fail for Cat5e, Cat6, Cat6a, and Cat8 at 100Mbps, 1Gbps, and 10Gbps.

Inputs

Send every one of these in inputs, in the units shown. Most are required: a call without one is refused (400) and costs nothing; one the calculator can do without takes the default shown. An input outside its range is still computed and flagged in the provenance.

Inputs of ethernet-cable
Name	Unit	Range	Default	Description
cableTypenumber	none	1 … 4	2	Cable CategoryOne of: 1 Cat5e · 2 Cat6 · 3 Cat6a · 4 Cat8
lengthnumber	m	1 … 500	50	Total cable run length in meters
speednumber	none	1 … 3	2	Network SpeedOne of: 1 100 Mbps (100BASE-TX) · 2 1 Gbps (1000BASE-T) · 3 10 Gbps (10GBASE-T)

Outputs

Returned in values, by key. A value that is unbounded or undefined is null.

Outputs of ethernet-cable
Field	Unit	Description
attenuationheadline	dB	Cable insertion loss at the PHY's signalling frequency (31.25, 62.5 or 400 MHz), from the TIA-568-C.2 horizontal-cable limit; Category 8 uses draft coefficients
maxLength	m	IEEE/TIA maximum cable length for this category and speed
headroom	m	Remaining length margin before limit (negative = over limit)
passOrFail	none	1 = within spec (PASS), 0 = exceeds maximum length (FAIL)

Calling it

Calculate: one call, the request and response in full, and its errors.
Batch: this calculator with others, or a sweep, in one request.
Solve for a target: the value of one input that brings an output to a target.

curl -X POST https://rftools.io/api/py/v1/calculate \
  -H "X-API-Key: $RFTOOLS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "slug": "ethernet-cable",
    "inputs": {
      "cableType": 2,
      "length": 50,
      "speed": 2
    }
  }'

import rftools

client = rftools.Client()  # reads RFTOOLS_API_KEY, or the key `rftools login` saved

result = client.calculate("ethernet-cable", {"cableType": 2, "length": 50, "speed": 2})
print(result.values)
print(result.warnings, result.provenance.formula_ref)

const response = await fetch("https://rftools.io/api/py/v1/calculate", {
  method: "POST",
  headers: {
    "X-API-Key": process.env.RFTOOLS_API_KEY,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "slug": "ethernet-cable",
    "inputs": {
      "cableType": 2,
      "length": 50,
      "speed": 2
    }
  }),
});
console.log(response.status, await response.json());

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	body := []byte(`{
	  "slug": "ethernet-cable",
	  "inputs": {
	    "cableType": 2,
	    "length": 50,
	    "speed": 2
	  }
	}`)
	req, err := http.NewRequest("POST", "https://rftools.io/api/py/v1/calculate", bytes.NewReader(body))
	if err != nil {
		panic(err)
	}
	req.Header.Set("X-API-Key", os.Getenv("RFTOOLS_API_KEY"))
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	out, _ := io.ReadAll(res.Body)
	fmt.Println(res.Status, string(out))
}

application/json

{
  "slug": "ethernet-cable",
  "values": {
    "attenuation": 7.690646622621211,
    "maxLength": 100,
    "headroom": 50,
    "passOrFail": 1
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:ethernet-cable",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "ANSI/TIA-568-C.2 (2009) Table 27, horizontal-cable insertion loss, carried into ANSI/TIA-568.2-D (2018); IEEE 802.3an-2006 and TIA TSB-155 (10GBASE-T: Category 6 to 55 m, 6A to 100 m, no Category 5e); IEEE 802.3bq channel model (Category 8 draft coefficients)",
    "assumptions": [
      {
        "code": "phy-signalling-frequency",
        "text": "The attenuation is the cable's insertion-loss limit at the PHY's signalling frequency: 31.25 MHz for 100BASE-TX, 62.5 MHz for 1000BASE-T and 400 MHz for 10GBASE-T."
      },
      {
        "code": "horizontal-cable-limit",
        "text": "The loss is the TIA-568-C.2 horizontal-cable limit per 100 m scaled to the length; patch cords and connectors are not added."
      },
      {
        "code": "cat8-draft-coefficients",
        "text": "Category 8 uses the draft d0.7 insertion-loss coefficients quoted by the IEEE 802.3bq channel model, and its 30 m channel at every speed."
      }
    ],
    "validRange": {
      "status": "inside",
      "bounds": {
        "cableType": {
          "min": 1,
          "max": 4,
          "unit": ""
        },
        "length": {
          "min": 1,
          "max": 500,
          "unit": "m"
        },
        "speed": {
          "min": 1,
          "max": 3,
          "unit": ""
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "cableType": 2,
      "length": 50,
      "speed": 2
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "cableType"
      ],
      "msg": "Input should be a valid number, unable to parse string as a number",
      "input": "abc"
    }
  ]
}

An input sent as text. Nothing was counted.

{
  "detail": "More than 120 requests in 60 seconds from this address.",
  "errorKind": "rate_limited",
  "limit": 120,
  "windowSeconds": 60,
  "upgradeUrl": "https://rftools.io/pricing/"
}

Too many requests in a minute, with Retry-After.

Same inputs on the calculator pageEthernet Cable Length & Attenuation Calculator, at these values