Documentation sections

RF Link Budget Calculator

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

Slug rf-link-budget. Free RF link budget calculator: enter Tx power, antenna gains, frequency, and distance to get received signal level, link margin, and max range. Covers satellite, terrestrial, and IoT links.

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 rf-link-budget
Name	Unit	Range	Default	Description
txPowernumber	dBm	−30 … 100	30	Transmitter output power
txGainnumber	dBi	−30 … 60	3	TX antenna gain in dBi
txCableLossnumber	dB	0 … 20	1	TX cable + connector losses (positive value)
frequencynumber	MHz	0.1 … 1000000	2400	Center frequency
distancenumber	km	0.001 … 1000000	1	Distance between TX and RX
rainFadenumber	dB	0 … 50	0	Rain attenuation per ITU-R P.838. Use 0 for line-of-sight ground links; 3–20 dB for satellite links above 10 GHz in heavy rain zones.
atmosphericLossnumber	dB	0 … 20	0.5	Gaseous absorption (O₂ at 60 GHz: ~15 dB/km; H₂O at 22 GHz: ~0.2 dB/km). Use 0.5 dB typical for sub-6 GHz terrestrial links.
pointingLossnumber	dB	0 … 10	0	Antenna misalignment loss. Pencil-beam dishes: 0.5–3 dB. Omnidirectional or wide-beam antennas: 0 dB.
extraLossCountnumber	none	0 … 4	0	How many extra loss terms the budget includes, such as polarisation mismatch, body loss or foliage
extraLoss1number	dB	0 … 50	0	An extra loss in the path, such as polarisation mismatch, body loss, foliage or a wall
extraLoss2number	dB	0 … 50	0	An extra loss in the path, such as polarisation mismatch, body loss, foliage or a wall
extraLoss3number	dB	0 … 50	0	An extra loss in the path, such as polarisation mismatch, body loss, foliage or a wall
extraLoss4number	dB	0 … 50	0	An extra loss in the path, such as polarisation mismatch, body loss, foliage or a wall
rxGainnumber	dBi	−30 … 60	3	RX antenna gain in dBi
rxCableLossnumber	dB	0 … 20	1	RX cable + connector losses
rxSensitivitynumber	dBm	−160 … 0	-90	Minimum receivable signal level
targetMarginnumber	dB	0 … 60	10	The fade margin the link must keep above the receiver sensitivity. The status passes at or above it and fails below 0 dB.

Outputs

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

Outputs of rf-link-budget
Field	Unit	Description
fspl	dB	Free Space Path Loss
eirp	dBm	Effective Isotropic Radiated Power
rxPower	dBm	Received Power
linkMarginheadline	dB	Link Margin
maxRangeKm	km	Max Range
totalAdditionalLoss	dB	Sum of rain fade, atmospheric loss, pointing loss and any extra loss terms
maxRangeAtTarget	km	The distance at which the link margin falls to the target margin
wavelength	mm	Wavelength
fresnelRadius	m	Radius of the first Fresnel zone at the middle of the path. Keep at least 60 % of it clear of obstacles.

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": "rf-link-budget",
    "inputs": {
      "txPower": 30,
      "txGain": 3,
      "txCableLoss": 1,
      "frequency": 2400,
      "distance": 1,
      "rainFade": 0,
      "atmosphericLoss": 0.5,
      "pointingLoss": 0,
      "extraLossCount": 0,
      "extraLoss1": 0,
      "extraLoss2": 0,
      "extraLoss3": 0,
      "extraLoss4": 0,
      "rxGain": 3,
      "rxCableLoss": 1,
      "rxSensitivity": -90,
      "targetMargin": 10
    }
  }'

import rftools

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

result = client.calculate("rf-link-budget", {
    "txPower": 30,
    "txGain": 3,
    "txCableLoss": 1,
    "frequency": 2400,
    "distance": 1,
    "rainFade": 0,
    "atmosphericLoss": 0.5,
    "pointingLoss": 0,
    "extraLossCount": 0,
    "extraLoss1": 0,
    "extraLoss2": 0,
    "extraLoss3": 0,
    "extraLoss4": 0,
    "rxGain": 3,
    "rxCableLoss": 1,
    "rxSensitivity": -90,
    "targetMargin": 10,
})
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": "rf-link-budget",
    "inputs": {
      "txPower": 30,
      "txGain": 3,
      "txCableLoss": 1,
      "frequency": 2400,
      "distance": 1,
      "rainFade": 0,
      "atmosphericLoss": 0.5,
      "pointingLoss": 0,
      "extraLossCount": 0,
      "extraLoss1": 0,
      "extraLoss2": 0,
      "extraLoss3": 0,
      "extraLoss4": 0,
      "rxGain": 3,
      "rxCableLoss": 1,
      "rxSensitivity": -90,
      "targetMargin": 10
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "rf-link-budget",
	  "inputs": {
	    "txPower": 30,
	    "txGain": 3,
	    "txCableLoss": 1,
	    "frequency": 2400,
	    "distance": 1,
	    "rainFade": 0,
	    "atmosphericLoss": 0.5,
	    "pointingLoss": 0,
	    "extraLossCount": 0,
	    "extraLoss1": 0,
	    "extraLoss2": 0,
	    "extraLoss3": 0,
	    "extraLoss4": 0,
	    "rxGain": 3,
	    "rxCableLoss": 1,
	    "rxSensitivity": -90,
	    "targetMargin": 10
	  }
	}`)
	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": "rf-link-budget",
  "values": {
    "fspl": 100.0520080561155,
    "eirp": 32,
    "rxPower": -66.5520080561155,
    "linkMargin": 23.447991943884503,
    "maxRangeKm": 14.873034905799756,
    "totalAdditionalLoss": 0.5,
    "wavelength": 124.91352416666666,
    "fresnelRadius": 5.588235950786855,
    "maxRangeAtTarget": 4.703266602151508
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:rf-link-budget",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "Friis, \"A Note on a Simple Transmission Formula\" (1946)",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "txPower": {
          "min": -30,
          "max": 100,
          "unit": "dBm"
        },
        "txGain": {
          "min": -30,
          "max": 60,
          "unit": "dBi"
        },
        "txCableLoss": {
          "min": 0,
          "max": 20,
          "unit": "dB"
        },
        "frequency": {
          "min": 0.1,
          "max": 1000000,
          "unit": "MHz"
        },
        "distance": {
          "min": 0.001,
          "max": 1000000,
          "unit": "km"
        },
        "rainFade": {
          "min": 0,
          "max": 50,
          "unit": "dB"
        },
        "atmosphericLoss": {
          "min": 0,
          "max": 20,
          "unit": "dB"
        },
        "pointingLoss": {
          "min": 0,
          "max": 10,
          "unit": "dB"
        },
        "extraLossCount": {
          "min": 0,
          "max": 4,
          "unit": ""
        },
        "extraLoss1": {
          "min": 0,
          "max": 50,
          "unit": "dB"
        },
        "extraLoss2": {
          "min": 0,
          "max": 50,
          "unit": "dB"
        },
        "extraLoss3": {
          "min": 0,
          "max": 50,
          "unit": "dB"
        },
        "extraLoss4": {
          "min": 0,
          "max": 50,
          "unit": "dB"
        },
        "rxGain": {
          "min": -30,
          "max": 60,
          "unit": "dBi"
        },
        "rxCableLoss": {
          "min": 0,
          "max": 20,
          "unit": "dB"
        },
        "rxSensitivity": {
          "min": -160,
          "max": 0,
          "unit": "dBm"
        },
        "targetMargin": {
          "min": 0,
          "max": 60,
          "unit": "dB"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "txPower": 30,
      "txGain": 3,
      "txCableLoss": 1,
      "frequency": 2400,
      "distance": 1,
      "rainFade": 0,
      "atmosphericLoss": 0.5,
      "pointingLoss": 0,
      "extraLossCount": 0,
      "extraLoss1": 0,
      "extraLoss2": 0,
      "extraLoss3": 0,
      "extraLoss4": 0,
      "rxGain": 3,
      "rxCableLoss": 1,
      "rxSensitivity": -90,
      "targetMargin": 10
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "txPower"
      ],
      "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 pageRF Link Budget Calculator, at these values