Documentation sections

ISM Band Wireless Coexistence Calculator

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

Slug ism-coexistence. Analyze collision probability and throughput impact when WiFi, Bluetooth, Zigbee, or LoRa share ISM bands. Enter duty cycles and channels. Free, instant results.

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 ism-coexistence
Name	Unit	Range	Default	Description
bandIndexnumber	none	0 … 4	0	ISM BandOne of: 0 2.4 GHz ISM (2400–2483.5 MHz) · 1 868 MHz (Europe, 863–870 MHz) · 2 915 MHz (Americas, 902–928 MHz) · 3 5.8 GHz ISM (5725–5850 MHz) · 4 433 MHz (Europe, 433.05–434.79 MHz)
dutyCycle1_pctnumber	%	0.01 … 100	50	WiFi at moderate load ≈ 20–60%, BLE advertising ≈ 0.5–5%, Zigbee ≈ 1%
channels1number	none	1 … 100	3	WiFi: 3 non-overlapping (1/6/11), BLE data: 37 channels, LoRaWAN EU: 8 channels
dutyCycle2_pctnumber	%	0.01 … 100	5	Protocol 2 Duty Cycle
channels2number	none	1 … 100	37	Protocol 2 Channels
txPowerOffset_dBnumber	dB	−30 … 40	10	Positive = Protocol 1 is stronger. WiFi (20 dBm) vs BLE (10 dBm) = +10 dB
channelWidth1_MHznumber	MHz	at least 0.001	20	Wi-Fi 20 MHz, Zigbee 2 MHz, LoRa 0.125 MHz. The plan spreads the channels evenly across the band
channelWidth2_MHznumber	MHz	at least 0.001	2	Bluetooth LE 2 MHz, Zigbee 2 MHz, LoRa 0.125 MHz

Outputs

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

Outputs of ism-coexistence
Field	Unit	Description
effectiveCollision_pctheadline	%	Effective Collision Rate
collisionProb_pct	%	Raw Collision Probability
throughputImpact_pct	%	Throughput Impact
sharedChannelFraction	%	Shared Channel Fraction
overlappingChannels	none	Protocol 2's channels that share spectrum with one of protocol 1's, with the channels spread evenly across the band: there a collision needs only both to transmit at once

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": "ism-coexistence",
    "inputs": {
      "bandIndex": 0,
      "dutyCycle1_pct": 50,
      "channels1": 3,
      "dutyCycle2_pct": 5,
      "channels2": 37,
      "txPowerOffset_dB": 10,
      "channelWidth1_MHz": 20,
      "channelWidth2_MHz": 2
    }
  }'

import rftools

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

result = client.calculate("ism-coexistence", {
    "bandIndex": 0,
    "dutyCycle1_pct": 50,
    "channels1": 3,
    "dutyCycle2_pct": 5,
    "channels2": 37,
    "txPowerOffset_dB": 10,
    "channelWidth1_MHz": 20,
    "channelWidth2_MHz": 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": "ism-coexistence",
    "inputs": {
      "bandIndex": 0,
      "dutyCycle1_pct": 50,
      "channels1": 3,
      "dutyCycle2_pct": 5,
      "channels2": 37,
      "txPowerOffset_dB": 10,
      "channelWidth1_MHz": 20,
      "channelWidth2_MHz": 2
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "ism-coexistence",
	  "inputs": {
	    "bandIndex": 0,
	    "dutyCycle1_pct": 50,
	    "channels1": 3,
	    "dutyCycle2_pct": 5,
	    "channels2": 37,
	    "txPowerOffset_dB": 10,
	    "channelWidth1_MHz": 20,
	    "channelWidth2_MHz": 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": "ism-coexistence",
  "values": {
    "collisionProb_pct": 0.12500000000000003,
    "effectiveCollision_pct": 0.08125000000000002,
    "throughputImpact_pct": 0.16250000000000003,
    "sharedChannelFraction": 5,
    "overlappingChannels": 29
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:ism-coexistence",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "ETSI EN 300 220-1 V3.1.1, Short Range Devices (SRD) — ISM band coexistence (2017)",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "bandIndex": {
          "min": 0,
          "max": 4,
          "unit": ""
        },
        "dutyCycle1_pct": {
          "min": 0.01,
          "max": 100,
          "unit": "%"
        },
        "channels1": {
          "min": 1,
          "max": 100,
          "unit": ""
        },
        "dutyCycle2_pct": {
          "min": 0.01,
          "max": 100,
          "unit": "%"
        },
        "channels2": {
          "min": 1,
          "max": 100,
          "unit": ""
        },
        "txPowerOffset_dB": {
          "min": -30,
          "max": 40,
          "unit": "dB"
        },
        "channelWidth1_MHz": {
          "min": 0.001,
          "max": null,
          "unit": "MHz"
        },
        "channelWidth2_MHz": {
          "min": 0.001,
          "max": null,
          "unit": "MHz"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "bandIndex": 0,
      "dutyCycle1_pct": 50,
      "channels1": 3,
      "dutyCycle2_pct": 5,
      "channels2": 37,
      "txPowerOffset_dB": 10,
      "channelWidth1_MHz": 20,
      "channelWidth2_MHz": 2
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "bandIndex"
      ],
      "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 pageISM Band Wireless Coexistence Calculator, at these values