Documentation sections

Embedded Resistor Calculator

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

Slug embedded-resistor. Calculate geometry for PCB embedded resistors from target resistance and sheet resistance. Supports NiP, TaN, CrSiO, and carbon materials.

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 embedded-resistor
Name	Unit	Range	Default	Description
targetResistancenumber	Ω	0.1 … 100000	100	Target Resistance
sheetResistancenumber	Ω/sq	0 … 10000	0	Sheet Resistance (0=auto from material)
widthnumber	mm	0.1 … 25	1	Resistor Width
trimAllowancenumber	%	0 … 50	10	Trim Allowance
materialnumber	none	0 … 4	0	MaterialOne of: 0 NiP 25 Ω/sq (Ohmega-Ply) · 1 NiP 100 Ω/sq · 2 TaN (100 Ω/sq) · 3 CrSiO (1000 Ω/sq) · 4 Carbon (100 Ω/sq)

Outputs

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

Outputs of embedded-resistor
Field	Unit	Description
numSquaresheadline	none	Number of Squares
length	mm	Resistor Length
designLength	mm	Design Length (pre-trim)
designResistance	Ω	Design Resistance (pre-trim)
area	mm²	Resistor Area
maxPower	mW	Max Power Dissipation
toleranceWithoutTrim	%	Tolerance (untrimmed)
toleranceWithTrim	%	Tolerance (trimmed)
aspectRatio	none	Aspect Ratio (L/W)

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": "embedded-resistor",
    "inputs": {
      "targetResistance": 100,
      "sheetResistance": 0,
      "width": 1,
      "trimAllowance": 10,
      "material": 0
    }
  }'

import rftools

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

result = client.calculate("embedded-resistor", {
    "targetResistance": 100,
    "sheetResistance": 0,
    "width": 1,
    "trimAllowance": 10,
    "material": 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": "embedded-resistor",
    "inputs": {
      "targetResistance": 100,
      "sheetResistance": 0,
      "width": 1,
      "trimAllowance": 10,
      "material": 0
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "embedded-resistor",
	  "inputs": {
	    "targetResistance": 100,
	    "sheetResistance": 0,
	    "width": 1,
	    "trimAllowance": 10,
	    "material": 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": "embedded-resistor",
  "values": {
    "numSquares": 4,
    "length": 4,
    "designLength": 3.6,
    "designResistance": 90,
    "area": 4,
    "maxPower": 100,
    "toleranceWithoutTrim": 10,
    "toleranceWithTrim": 5,
    "aspectRatio": 4
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:embedded-resistor",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "targetResistance": {
          "min": 0.1,
          "max": 100000,
          "unit": "Ω"
        },
        "sheetResistance": {
          "min": 0,
          "max": 10000,
          "unit": "Ω/sq"
        },
        "width": {
          "min": 0.1,
          "max": 25,
          "unit": "mm"
        },
        "trimAllowance": {
          "min": 0,
          "max": 50,
          "unit": "%"
        },
        "material": {
          "min": 0,
          "max": 4,
          "unit": ""
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "targetResistance": 100,
      "sheetResistance": 0,
      "width": 1,
      "trimAllowance": 10,
      "material": 0
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "targetResistance"
      ],
      "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 pageEmbedded Resistor Calculator, at these values