Documentation sections

Via Voltage Drop & Power Calculator

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

Slug via-voltage-drop. Calculate DC resistance, voltage drop, and power dissipation of plated through-hole vias with temperature compensation and parallel via arrays.

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 via-voltage-drop
Name	Unit	Range	Default	Description
drillDiameternumber	mm	0.1 … 1	0.3	Drill Diameter
platingThicknessnumber	µm	12 … 50	25	Plating Thickness
viaLengthnumber	mm	0.1 … 6	1.6	Via Length (board thickness)
currentnumber	A	0.001 … 50	1	Current
temperaturenumber	°C	−40 … 125	25	Operating Temperature
numViasnumber	none	1 … 100	1	Number of Parallel Vias

Outputs

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

Outputs of via-voltage-drop
Field	Unit	Description
rSingleMOhm	mΩ	Single Via Resistance
rTotalMOhm	mΩ	Total Resistance (parallel)
vDropMVheadline	mV	Voltage Drop
pDissipationMW	mW	Power Dissipation
areaMm2	mm²	Via Cross-Section
deltaT	°C	Peak rise of a barrel heated along its length with both ends at the pad temperature: P·L/(8·k·A·N)
thetaVia	°C/W	Thermal 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": "via-voltage-drop",
    "inputs": {
      "drillDiameter": 0.3,
      "platingThickness": 25,
      "viaLength": 1.6,
      "current": 1,
      "temperature": 25,
      "numVias": 1
    }
  }'

import rftools

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

result = client.calculate("via-voltage-drop", {
    "drillDiameter": 0.3,
    "platingThickness": 25,
    "viaLength": 1.6,
    "current": 1,
    "temperature": 25,
    "numVias": 1,
})
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": "via-voltage-drop",
    "inputs": {
      "drillDiameter": 0.3,
      "platingThickness": 25,
      "viaLength": 1.6,
      "current": 1,
      "temperature": 25,
      "numVias": 1
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "via-voltage-drop",
	  "inputs": {
	    "drillDiameter": 0.3,
	    "platingThickness": 25,
	    "viaLength": 1.6,
	    "current": 1,
	    "temperature": 25,
	    "numVias": 1
	  }
	}`)
	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": "via-voltage-drop",
  "values": {
    "rSingleMOhm": 1.3023284782838458,
    "rTotalMOhm": 1.3023284782838458,
    "vDropMV": 1.3023284782838458,
    "pDissipationMW": 1.3023284782838458,
    "areaMm2": 0.021598449493429827,
    "deltaT": 0.03132327969370978,
    "thetaVia": 192.41400439917456
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:via-voltage-drop",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "Resistance R = ρL/A with ρ₂₀ = 1/58 Ω·mm²/m (IEC 60028); self-heating: Incropera, DeWitt, Bergman & Lavine, Fundamentals of Heat and Mass Transfer, 7th ed., section 3.5 (one-dimensional conduction with uniform generation)",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "drillDiameter": {
          "min": 0.1,
          "max": 1,
          "unit": "mm"
        },
        "platingThickness": {
          "min": 12,
          "max": 50,
          "unit": "µm"
        },
        "viaLength": {
          "min": 0.1,
          "max": 6,
          "unit": "mm"
        },
        "current": {
          "min": 0.001,
          "max": 50,
          "unit": "A"
        },
        "temperature": {
          "min": -40,
          "max": 125,
          "unit": "°C"
        },
        "numVias": {
          "min": 1,
          "max": 100,
          "unit": ""
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "drillDiameter": 0.3,
      "platingThickness": 25,
      "viaLength": 1.6,
      "current": 1,
      "temperature": 25,
      "numVias": 1
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "drillDiameter"
      ],
      "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 pageVia Voltage Drop & Power Calculator, at these values