Documentation sections

Radiated Emission Estimate

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

Slug radiated-emission-estimate. Estimate radiated emissions from PCB current loops using the small-loop model. Compare the E-field against CISPR 32 or FCC Class A and B limits instantly.

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 radiated-emission-estimate
Name	Unit	Range	Default	Description
currentnumber	mA	at least 0.001	10	Loop Current (peak)
loopAreanumber	cm²	at least 0.001	1	Area enclosed by the current loop on PCB
frequencynumber	MHz	at least 0.01	100	Frequency
distancenumber	m	at least 0.1	3	CISPR 32 and FCC Part 15 measure at 3 m or 10 m; other distances scale at 20 dB/decade
standardnumber	none	0 … 1	0	The radiated-emission limits the field is checked againstOne of: 0 CISPR 32 · 1 FCC §15.109
emissionClassnumber	none	0 … 1	0	Class B: residential equipment, the stricter limit. Class A: commercial and industrial equipmentOne of: 0 Class B · 1 Class A

Outputs

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

Outputs of radiated-emission-estimate
Field	Unit	Description
eFieldDbuvMheadline	dBμV/m	E-Field
margin	dB	The limit of the chosen standard and class at this frequency and distance, minus the field; below 0 dB does not comply
eFieldUvm	µV/m	The field in µV/m, the unit the FCC writes its limits in
limitField	µV/m	The limit of the chosen standard and class at this frequency, at the measurement distance
limitPercent	%	The field as a percentage of the limit; above 100 % does not comply (200 % is 6 dB over)
maxCurrent	mA	The loop current at which the field equals the limit; at or below it the emission complies
maxLoopArea	cm²	The loop area at which the field equals the limit; at or below it the emission complies

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": "radiated-emission-estimate",
    "inputs": {
      "current": 10,
      "loopArea": 1,
      "frequency": 100,
      "distance": 3,
      "standard": 0,
      "emissionClass": 0
    }
  }'

import rftools

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

result = client.calculate("radiated-emission-estimate", {
    "current": 10,
    "loopArea": 1,
    "frequency": 100,
    "distance": 3,
    "standard": 0,
    "emissionClass": 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": "radiated-emission-estimate",
    "inputs": {
      "current": 10,
      "loopArea": 1,
      "frequency": 100,
      "distance": 3,
      "standard": 0,
      "emissionClass": 0
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "radiated-emission-estimate",
	  "inputs": {
	    "current": 10,
	    "loopArea": 1,
	    "frequency": 100,
	    "distance": 3,
	    "standard": 0,
	    "emissionClass": 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": "radiated-emission-estimate",
  "values": {
    "eFieldDbuvM": 32.84835558137281,
    "margin": 7.151644418627193,
    "eFieldUvm": 43.895275493507626,
    "limitField": 100,
    "limitPercent": 43.895275493507626,
    "maxCurrent": 22.78149501870437,
    "maxLoopArea": 2.278149501870437
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:radiated-emission-estimate",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "Ott, Electromagnetic Compatibility Engineering (2009), ch. 12; CISPR 32:2015+AMD1:2019 Annex A, Tables A.4 and A.5 (class B)",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "current": {
          "min": 0.001,
          "max": null,
          "unit": "mA"
        },
        "loopArea": {
          "min": 0.001,
          "max": null,
          "unit": "cm²"
        },
        "frequency": {
          "min": 0.01,
          "max": null,
          "unit": "MHz"
        },
        "distance": {
          "min": 0.1,
          "max": null,
          "unit": "m"
        },
        "standard": {
          "min": 0,
          "max": 1,
          "unit": ""
        },
        "emissionClass": {
          "min": 0,
          "max": 1,
          "unit": ""
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "current": 10,
      "loopArea": 1,
      "frequency": 100,
      "distance": 3,
      "standard": 0,
      "emissionClass": 0
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "current"
      ],
      "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 pageRadiated Emission Estimate, at these values