Documentation sections

EMI Margin Budget

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

Slug emi-margin-budget. Calculate EMI compliance margin with measurement uncertainty and safety margin. Predict CISPR/FCC pre-compliance test pass or fail 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 emi-margin-budget
Name	Unit	Range	Default	Description
measuredLevelnumber	dBμV/m	at least −100	30	Measured Emission Level
limitLevelnumber	dBμV/m	at least −100	40	CISPR 22 Class B radiated: 40 dBμV/m (30–230 MHz) at 3m
measurementUncertaintynumber	dB	at least 0	6	Typically 6 dB for pre-compliance setups
safetyMarginnumber	dB	at least 0	6	Design Safety Margin
marginTermsnumber	none	0 … 6	0	How many further allowances the budget holds back (0–6)
term1Allowancenumber	dB	0 … 40	0	A further allowance held back from the margin, such as unit-to-unit spread, cable layout or the correlation between a pre-compliance set-up and the accredited site
term2Allowancenumber	dB	0 … 40	0	A further allowance held back from the margin, such as unit-to-unit spread, cable layout or the correlation between a pre-compliance set-up and the accredited site
term3Allowancenumber	dB	0 … 40	0	A further allowance held back from the margin, such as unit-to-unit spread, cable layout or the correlation between a pre-compliance set-up and the accredited site
term4Allowancenumber	dB	0 … 40	0	A further allowance held back from the margin, such as unit-to-unit spread, cable layout or the correlation between a pre-compliance set-up and the accredited site
term5Allowancenumber	dB	0 … 40	0	A further allowance held back from the margin, such as unit-to-unit spread, cable layout or the correlation between a pre-compliance set-up and the accredited site
term6Allowancenumber	dB	0 … 40	0	A further allowance held back from the margin, such as unit-to-unit spread, cable layout or the correlation between a pre-compliance set-up and the accredited site

Outputs

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

Outputs of emi-margin-budget
Field	Unit	Description
rawMargin	dB	Raw Margin
adjustedMarginheadline	dB	Adjusted Margin
requiredReduction	dB	Reduction Required
totalAllowance	dB	Measurement uncertainty, safety margin and every further allowance, 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": "emi-margin-budget",
    "inputs": {
      "measuredLevel": 30,
      "limitLevel": 40,
      "measurementUncertainty": 6,
      "safetyMargin": 6,
      "marginTerms": 0,
      "term1Allowance": 0,
      "term2Allowance": 0,
      "term3Allowance": 0,
      "term4Allowance": 0,
      "term5Allowance": 0,
      "term6Allowance": 0
    }
  }'

import rftools

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

result = client.calculate("emi-margin-budget", {
    "measuredLevel": 30,
    "limitLevel": 40,
    "measurementUncertainty": 6,
    "safetyMargin": 6,
    "marginTerms": 0,
    "term1Allowance": 0,
    "term2Allowance": 0,
    "term3Allowance": 0,
    "term4Allowance": 0,
    "term5Allowance": 0,
    "term6Allowance": 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": "emi-margin-budget",
    "inputs": {
      "measuredLevel": 30,
      "limitLevel": 40,
      "measurementUncertainty": 6,
      "safetyMargin": 6,
      "marginTerms": 0,
      "term1Allowance": 0,
      "term2Allowance": 0,
      "term3Allowance": 0,
      "term4Allowance": 0,
      "term5Allowance": 0,
      "term6Allowance": 0
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "emi-margin-budget",
	  "inputs": {
	    "measuredLevel": 30,
	    "limitLevel": 40,
	    "measurementUncertainty": 6,
	    "safetyMargin": 6,
	    "marginTerms": 0,
	    "term1Allowance": 0,
	    "term2Allowance": 0,
	    "term3Allowance": 0,
	    "term4Allowance": 0,
	    "term5Allowance": 0,
	    "term6Allowance": 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": "emi-margin-budget",
  "values": {
    "rawMargin": 10,
    "adjustedMargin": -2,
    "requiredReduction": 2,
    "totalAllowance": 12
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:emi-margin-budget",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "measuredLevel": {
          "min": -100,
          "max": null,
          "unit": "dBμV/m"
        },
        "limitLevel": {
          "min": -100,
          "max": null,
          "unit": "dBμV/m"
        },
        "measurementUncertainty": {
          "min": 0,
          "max": null,
          "unit": "dB"
        },
        "safetyMargin": {
          "min": 0,
          "max": null,
          "unit": "dB"
        },
        "marginTerms": {
          "min": 0,
          "max": 6,
          "unit": ""
        },
        "term1Allowance": {
          "min": 0,
          "max": 40,
          "unit": "dB"
        },
        "term2Allowance": {
          "min": 0,
          "max": 40,
          "unit": "dB"
        },
        "term3Allowance": {
          "min": 0,
          "max": 40,
          "unit": "dB"
        },
        "term4Allowance": {
          "min": 0,
          "max": 40,
          "unit": "dB"
        },
        "term5Allowance": {
          "min": 0,
          "max": 40,
          "unit": "dB"
        },
        "term6Allowance": {
          "min": 0,
          "max": 40,
          "unit": "dB"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "measuredLevel": 30,
      "limitLevel": 40,
      "measurementUncertainty": 6,
      "safetyMargin": 6,
      "marginTerms": 0,
      "term1Allowance": 0,
      "term2Allowance": 0,
      "term3Allowance": 0,
      "term4Allowance": 0,
      "term5Allowance": 0,
      "term6Allowance": 0
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "measuredLevel"
      ],
      "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 pageEMI Margin Budget, at these values