Documentation sections

LoRa Link Budget Calculator — Sensitivity, Time on Air & Range

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

Slug lora-link-budget. LoRa link budget from the Semtech SX1276 formulas: receiver sensitivity by spreading factor and bandwidth, symbol time, time on air with automatic low-data-rate optimisation, duty-cycle off-time, free-space or Okumura–Hata path loss, link margin and maximum range.

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 lora-link-budget
Name	Unit	Range	Default	Description
spreadingFactornumber	none	6 … 12	9	Chips per symbol are 2^SF; each step up adds about 2.5 dB of sensitivity and doubles the airtime
bandwidthnumber	kHz	at least 7.8	125	LoRa signal bandwidth; 125 kHz in most LoRaWAN channels
codingRatenumber	none	1 … 4	1	Forward error correction: four data bits in five to eight coded bitsOne of: 1 4/5 · 2 4/6 · 3 4/7 · 4 4/8
payloadLengthnumber	bytes	1 … 255	20	Bytes in the LoRa payload, 1 to 255 (a LoRaWAN frame adds 13 bytes of overhead to the application data)
preambleLengthnumber	symbols	at least 0	8	Programmed preamble symbols; 8 in LoRaWAN
implicitHeadernumber	none	0 … 1	0	Header ModeOne of: 0 Explicit header · 1 Implicit header
crcnumber	none	0 … 1	1	Payload CRCOne of: 1 CRC on · 0 CRC off
noiseFigurenumber	dB	at least 0	6	About 6 dB for an SX127x with highest LNA gain
txPowernumber	dBm	any	14	14 dBm is the usual EU 868 MHz limit; 20 dBm with PA_BOOST
txGainnumber	dBi	any	2.15	Transmit Antenna Gain
rxGainnumber	dBi	any	5	Receive Antenna Gain
lossesnumber	dB	at least 0	2	Cable & Other Losses
frequencynumber	MHz	at least 1	868	Frequency
pathLossModelnumber	none	0 … 5	1	Free space, or Okumura–Hata for an urban, suburban or rural pathOne of: 0 Free space · 1 Okumura–Hata, urban (small/medium city) · 2 Okumura–Hata, urban (large city) · 3 Okumura–Hata, suburban · 4 Okumura–Hata, rural quasi-open · 5 Okumura–Hata, rural open
distancenumber	km	at least 0.001	2	Distance
baseHeightnumber	m	at least 1	30	Used by Okumura–Hata, which covers 30 to 200 m
mobileHeightnumber	m	at least 0.1	1.5	Used by Okumura–Hata, which covers 1 to 10 m
dutyCyclenumber	%	0.001 … 100	1	Share of time a device may transmit; 1% in the EU 868.0–868.6 MHz sub-band (ETSI EN 300 220-2)
extraLossCountnumber	none	0 … 6	0	How many further losses the link adds, such as building entry, foliage, body or polarisation mismatch (0–6)
extraLoss1number	dB	0 … 50	0	A further loss on the link, such as building entry, foliage, body loss or polarisation mismatch
extraLoss2number	dB	0 … 50	0	A further loss on the link, such as building entry, foliage, body loss or polarisation mismatch
extraLoss3number	dB	0 … 50	0	A further loss on the link, such as building entry, foliage, body loss or polarisation mismatch
extraLoss4number	dB	0 … 50	0	A further loss on the link, such as building entry, foliage, body loss or polarisation mismatch
extraLoss5number	dB	0 … 50	0	A further loss on the link, such as building entry, foliage, body loss or polarisation mismatch
extraLoss6number	dB	0 … 50	0	A further loss on the link, such as building entry, foliage, body loss or polarisation mismatch

Outputs

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

Outputs of lora-link-budget
Field	Unit	Description
linkMarginheadline	dB	Link Margin
sensitivity	dBm	Receiver Sensitivity
receivedPower	dBm	Received Power
pathLoss	dB	Path Loss
maxRange	km	Maximum Range
timeOnAir	ms	Time on Air
symbolTime	ms	Symbol Time
payloadSymbols	none	Payload Symbols
lowDataRateOptimize	none	Low-Data-Rate Optimisation (1 = On)
bitRate	bit/s	Equivalent Bit Rate
offTime	s	Minimum Off-Time After Each Packet
packetsPerHour	none	Packets per Hour at the Duty Cycle
totalLoss	dB	The cable and other losses, the path loss and every extra loss, added

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": "lora-link-budget",
    "inputs": {
      "spreadingFactor": 9,
      "bandwidth": 125,
      "codingRate": 1,
      "payloadLength": 20,
      "preambleLength": 8,
      "implicitHeader": 0,
      "crc": 1,
      "noiseFigure": 6,
      "txPower": 14,
      "txGain": 2.15,
      "rxGain": 5,
      "losses": 2,
      "frequency": 868,
      "pathLossModel": 1,
      "distance": 2,
      "baseHeight": 30,
      "mobileHeight": 1.5,
      "dutyCycle": 1,
      "extraLossCount": 0,
      "extraLoss1": 0,
      "extraLoss2": 0,
      "extraLoss3": 0,
      "extraLoss4": 0,
      "extraLoss5": 0,
      "extraLoss6": 0
    }
  }'

import rftools

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

result = client.calculate("lora-link-budget", {
    "spreadingFactor": 9,
    "bandwidth": 125,
    "codingRate": 1,
    "payloadLength": 20,
    "preambleLength": 8,
    "implicitHeader": 0,
    "crc": 1,
    "noiseFigure": 6,
    "txPower": 14,
    "txGain": 2.15,
    "rxGain": 5,
    "losses": 2,
    "frequency": 868,
    "pathLossModel": 1,
    "distance": 2,
    "baseHeight": 30,
    "mobileHeight": 1.5,
    "dutyCycle": 1,
    "extraLossCount": 0,
    "extraLoss1": 0,
    "extraLoss2": 0,
    "extraLoss3": 0,
    "extraLoss4": 0,
    "extraLoss5": 0,
    "extraLoss6": 0,
})
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": "lora-link-budget",
    "inputs": {
      "spreadingFactor": 9,
      "bandwidth": 125,
      "codingRate": 1,
      "payloadLength": 20,
      "preambleLength": 8,
      "implicitHeader": 0,
      "crc": 1,
      "noiseFigure": 6,
      "txPower": 14,
      "txGain": 2.15,
      "rxGain": 5,
      "losses": 2,
      "frequency": 868,
      "pathLossModel": 1,
      "distance": 2,
      "baseHeight": 30,
      "mobileHeight": 1.5,
      "dutyCycle": 1,
      "extraLossCount": 0,
      "extraLoss1": 0,
      "extraLoss2": 0,
      "extraLoss3": 0,
      "extraLoss4": 0,
      "extraLoss5": 0,
      "extraLoss6": 0
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "lora-link-budget",
	  "inputs": {
	    "spreadingFactor": 9,
	    "bandwidth": 125,
	    "codingRate": 1,
	    "payloadLength": 20,
	    "preambleLength": 8,
	    "implicitHeader": 0,
	    "crc": 1,
	    "noiseFigure": 6,
	    "txPower": 14,
	    "txGain": 2.15,
	    "rxGain": 5,
	    "losses": 2,
	    "frequency": 868,
	    "pathLossModel": 1,
	    "distance": 2,
	    "baseHeight": 30,
	    "mobileHeight": 1.5,
	    "dutyCycle": 1,
	    "extraLossCount": 0,
	    "extraLoss1": 0,
	    "extraLoss2": 0,
	    "extraLoss3": 0,
	    "extraLoss4": 0,
	    "extraLoss5": 0,
	    "extraLoss6": 0
	  }
	}`)
	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": "lora-link-budget",
  "values": {
    "linkMargin": 12.058955385826835,
    "sensitivity": -129.50608706414752,
    "receivedPower": -117.44713167832069,
    "pathLoss": 136.5971316783207,
    "maxRange": 4.399184913581315,
    "timeOnAir": 185.344,
    "symbolTime": 4.096,
    "payloadSymbols": 33,
    "lowDataRateOptimize": 0,
    "bitRate": 1757.8125,
    "offTime": 18.349055999999997,
    "packetsPerHour": 194.23342541436466,
    "totalLoss": 138.5971316783207
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:lora-link-budget",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "Semtech SX1276/77/78/79 datasheet Rev. 4 (2015), Table 13, §4.1.1.5–4.1.1.7; Semtech AN1200.13 Rev. 1 (2013), Eqn. 1; Hata (1980); ITU-R P.525-4",
    "assumptions": [
      {
        "code": "sx1276-snr-limits",
        "text": "Sensitivity uses the SX1276/77/78/79 demodulator SNR limits by spreading factor and the noise figure entered; another LoRa radio may differ by a dB or two."
      },
      {
        "code": "automatic-ldro",
        "text": "Low-data-rate optimisation is switched on exactly when the symbol time exceeds 16 ms, as the datasheet mandates."
      },
      {
        "code": "median-path-loss",
        "text": "Path loss is the free-space or Okumura–Hata median, with no fade margin; the link margin is what is left for fading."
      }
    ],
    "validRange": {
      "status": "inside",
      "bounds": {
        "spreadingFactor": {
          "min": 6,
          "max": 12,
          "unit": ""
        },
        "bandwidth": {
          "min": 7.8,
          "max": null,
          "unit": "kHz"
        },
        "codingRate": {
          "min": 1,
          "max": 4,
          "unit": ""
        },
        "payloadLength": {
          "min": 1,
          "max": 255,
          "unit": "bytes"
        },
        "preambleLength": {
          "min": 0,
          "max": null,
          "unit": "symbols"
        },
        "implicitHeader": {
          "min": 0,
          "max": 1,
          "unit": ""
        },
        "crc": {
          "min": 0,
          "max": 1,
          "unit": ""
        },
        "noiseFigure": {
          "min": 0,
          "max": null,
          "unit": "dB"
        },
        "txPower": {
          "min": null,
          "max": null,
          "unit": "dBm"
        },
        "txGain": {
          "min": null,
          "max": null,
          "unit": "dBi"
        },
        "rxGain": {
          "min": null,
          "max": null,
          "unit": "dBi"
        },
        "losses": {
          "min": 0,
          "max": null,
          "unit": "dB"
        },
        "frequency": {
          "min": 1,
          "max": null,
          "unit": "MHz"
        },
        "pathLossModel": {
          "min": 0,
          "max": 5,
          "unit": ""
        },
        "distance": {
          "min": 0.001,
          "max": null,
          "unit": "km"
        },
        "baseHeight": {
          "min": 1,
          "max": null,
          "unit": "m"
        },
        "mobileHeight": {
          "min": 0.1,
          "max": null,
          "unit": "m"
        },
        "dutyCycle": {
          "min": 0.001,
          "max": 100,
          "unit": "%"
        },
        "extraLossCount": {
          "min": 0,
          "max": 6,
          "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"
        },
        "extraLoss5": {
          "min": 0,
          "max": 50,
          "unit": "dB"
        },
        "extraLoss6": {
          "min": 0,
          "max": 50,
          "unit": "dB"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "spreadingFactor": 9,
      "bandwidth": 125,
      "codingRate": 1,
      "payloadLength": 20,
      "preambleLength": 8,
      "implicitHeader": 0,
      "crc": 1,
      "noiseFigure": 6,
      "txPower": 14,
      "txGain": 2.15,
      "rxGain": 5,
      "losses": 2,
      "frequency": 868,
      "pathLossModel": 1,
      "distance": 2,
      "baseHeight": 30,
      "mobileHeight": 1.5,
      "dutyCycle": 1,
      "extraLossCount": 0,
      "extraLoss1": 0,
      "extraLoss2": 0,
      "extraLoss3": 0,
      "extraLoss4": 0,
      "extraLoss5": 0,
      "extraLoss6": 0
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "spreadingFactor"
      ],
      "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 pageLoRa Link Budget Calculator — Sensitivity, Time on Air & Range, at these values