Documentation sections

EIRP / ERP Regulatory Calculator

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

Slug eirp-calculator. Calculate EIRP and ERP from transmit power, cable loss, and antenna gain. Check FCC Part 15 and ETSI regulatory compliance margins. 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 eirp-calculator
Name	Unit	Range	Default	Description
txPower_dbmnumber	dBm	−30 … 60	20	Transmitter output power at the RF connector
cableLoss_dbnumber	dB	0 … 30	1	Total feedline and connector losses (positive value)
antennaGain_dbinumber	dBi	−20 … 40	2.15	Antenna gain in dBi; 2.15 dBi = half-wave dipole
regulatoryLimit_dbmnumber	dBm	−20 … 60	36	Maximum permitted EIRP per applicable regulation

Outputs

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

Outputs of eirp-calculator
Field	Unit	Description
eirp_dbmheadline	dBm	Effective Isotropic Radiated Power = P_TX − L_cable + G_ant
erp_dbm	dBm	Effective Radiated Power (relative to half-wave dipole): EIRP − 2.15 dB
eirp_w	W	EIRP in watts
margin_db	dB	Headroom below the regulatory limit; negative = non-compliant
maxPermittedGain_dbi	dBi	Highest antenna gain that keeps EIRP within the regulatory limit

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": "eirp-calculator",
    "inputs": {
      "txPower_dbm": 20,
      "cableLoss_db": 1,
      "antennaGain_dbi": 2.15,
      "regulatoryLimit_dbm": 36
    }
  }'

import rftools

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

result = client.calculate("eirp-calculator", {
    "txPower_dbm": 20,
    "cableLoss_db": 1,
    "antennaGain_dbi": 2.15,
    "regulatoryLimit_dbm": 36,
})
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": "eirp-calculator",
    "inputs": {
      "txPower_dbm": 20,
      "cableLoss_db": 1,
      "antennaGain_dbi": 2.15,
      "regulatoryLimit_dbm": 36
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "eirp-calculator",
	  "inputs": {
	    "txPower_dbm": 20,
	    "cableLoss_db": 1,
	    "antennaGain_dbi": 2.15,
	    "regulatoryLimit_dbm": 36
	  }
	}`)
	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": "eirp-calculator",
  "values": {
    "eirp_dbm": 21.15,
    "erp_dbm": 19,
    "eirp_w": 0.1303166778452299,
    "margin_db": 14.850000000000001,
    "maxPermittedGain_dbi": 17
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:eirp-calculator",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "FCC Part 15 §15.247; ETSI EN 300 328; IEEE Std 149-1979",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "txPower_dbm": {
          "min": -30,
          "max": 60,
          "unit": "dBm"
        },
        "cableLoss_db": {
          "min": 0,
          "max": 30,
          "unit": "dB"
        },
        "antennaGain_dbi": {
          "min": -20,
          "max": 40,
          "unit": "dBi"
        },
        "regulatoryLimit_dbm": {
          "min": -20,
          "max": 60,
          "unit": "dBm"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "txPower_dbm": 20,
      "cableLoss_db": 1,
      "antennaGain_dbi": 2.15,
      "regulatoryLimit_dbm": 36
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "txPower_dbm"
      ],
      "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 pageEIRP / ERP Regulatory Calculator, at these values