Documentation sections

PCB Trace Resistance Calculator

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

Slug trace-resistance. Calculate PCB copper trace DC resistance from width, length, thickness, and temperature. Get sheet resistance and temp coefficient. 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 trace-resistance
Name	Unit	Range	Default	Description
traceWidthnumber	mm	0.05 … 50	0.5	Trace Width
traceLengthnumber	mm	0.1 … 10000	100	Trace Length
copperThicknessnumber	μm	1 … 200	35	Copper Thickness
temperaturenumber	°C	−55 … 150	25	Temperature

Outputs

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

Outputs of trace-resistance
Field	Unit	Description
resistanceheadline	Ω	Resistance
resistanceMOhm	mΩ	Resistance
sheetResistance	mΩ/□	Sheet Resistance

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": "trace-resistance",
    "inputs": {
      "traceWidth": 0.5,
      "traceLength": 100,
      "copperThickness": 35,
      "temperature": 25
    }
  }'

import rftools

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

result = client.calculate("trace-resistance", {
    "traceWidth": 0.5,
    "traceLength": 100,
    "copperThickness": 35,
    "temperature": 25,
})
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": "trace-resistance",
    "inputs": {
      "traceWidth": 0.5,
      "traceLength": 100,
      "copperThickness": 35,
      "temperature": 25
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "trace-resistance",
	  "inputs": {
	    "traceWidth": 0.5,
	    "traceLength": 100,
	    "copperThickness": 35,
	    "temperature": 25
	  }
	}`)
	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": "trace-resistance",
  "values": {
    "resistance": 0.10045812807881774,
    "resistanceMOhm": 100.45812807881774,
    "sheetResistance": 0.5022906403940887
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:trace-resistance",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "IPC-2221B; copper ρ₂₀ = 1/58 Ω·mm²/m = 1.7241×10⁻⁸ Ω·m (IEC 60028), α = 3.93×10⁻³ /°C",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "traceWidth": {
          "min": 0.05,
          "max": 50,
          "unit": "mm"
        },
        "traceLength": {
          "min": 0.1,
          "max": 10000,
          "unit": "mm"
        },
        "copperThickness": {
          "min": 1,
          "max": 200,
          "unit": "μm"
        },
        "temperature": {
          "min": -55,
          "max": 150,
          "unit": "°C"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "traceWidth": 0.5,
      "traceLength": 100,
      "copperThickness": 35,
      "temperature": 25
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "traceWidth"
      ],
      "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 pagePCB Trace Resistance Calculator, at these values