Documentation sections

Series / Parallel Resistor, Capacitor & Inductor Calculator

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

Slug series-parallel-resistor. Calculate the equivalent series and parallel combination of up to eight resistors, capacitors, or inductors. Also computes the voltage divider ratio for two-resistor networks.

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 series-parallel-resistor
Name	Unit	Range	Default	Description
r1number	Ω	0 … 1000000000	1000	R1 (or C1 in nF / L1 in μH)
r2number	Ω	0 … 1000000000	1000	R2 (or C2 in nF / L2 in μH)
r3number	Ω	0 … 1000000000	0	Set to 0 to ignore. R3 for 3-resistor combinations.
r4number	Ω	0 … 1000000000	0	Set to 0 to ignore.
r5number	Ω	0 … 1000000000	0	Set to 0 to ignore.
r6number	Ω	0 … 1000000000	0	Set to 0 to ignore.
r7number	Ω	0 … 1000000000	0	Set to 0 to ignore.
r8number	Ω	0 … 1000000000	0	Set to 0 to ignore.
numPartsnumber	none	1 … 8	4	How many of R1–R8 are in the network (1–8); a position set to 0 is ignored
componentTypenumber	none	0 … 2	0	Component TypeOne of: 0 Resistor (Ω) · 1 Capacitor (nF) · 2 Inductor (μH)

Outputs

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

Outputs of series-parallel-resistor
Field	Unit	Description
seriesTotalheadline	Ω / nF / μH	Series Resistance (Ω) / Series Capacitance (nF) / Series Inductance (μH)
parallelTotal	Ω / nF / μH	Parallel Resistance (Ω) / Parallel Capacitance (nF) / Parallel Inductance (μH)
voltDividerRatio	V/V	Output voltage as a fraction of input voltage (Vout/Vin = R2/(R1+R2)). Only valid for two-resistor networks.
sumOfValues	Ω / nF / μH	The plain sum of the parts in use: the series total of resistors or inductors, the parallel total of capacitors. Each part’s share is its part of this sum.

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": "series-parallel-resistor",
    "inputs": {
      "r1": 1000,
      "r2": 1000,
      "r3": 0,
      "r4": 0,
      "r5": 0,
      "r6": 0,
      "r7": 0,
      "r8": 0,
      "numParts": 4,
      "componentType": 0
    }
  }'

import rftools

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

result = client.calculate("series-parallel-resistor", {
    "r1": 1000,
    "r2": 1000,
    "r3": 0,
    "r4": 0,
    "r5": 0,
    "r6": 0,
    "r7": 0,
    "r8": 0,
    "numParts": 4,
    "componentType": 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": "series-parallel-resistor",
    "inputs": {
      "r1": 1000,
      "r2": 1000,
      "r3": 0,
      "r4": 0,
      "r5": 0,
      "r6": 0,
      "r7": 0,
      "r8": 0,
      "numParts": 4,
      "componentType": 0
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "series-parallel-resistor",
	  "inputs": {
	    "r1": 1000,
	    "r2": 1000,
	    "r3": 0,
	    "r4": 0,
	    "r5": 0,
	    "r6": 0,
	    "r7": 0,
	    "r8": 0,
	    "numParts": 4,
	    "componentType": 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": "series-parallel-resistor",
  "values": {
    "seriesTotal": 2000,
    "parallelTotal": 500,
    "voltDividerRatio": 0.5,
    "sumOfValues": 2000
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:series-parallel-resistor",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "r1": {
          "min": 0,
          "max": 1000000000,
          "unit": "Ω"
        },
        "r2": {
          "min": 0,
          "max": 1000000000,
          "unit": "Ω"
        },
        "r3": {
          "min": 0,
          "max": 1000000000,
          "unit": "Ω"
        },
        "r4": {
          "min": 0,
          "max": 1000000000,
          "unit": "Ω"
        },
        "r5": {
          "min": 0,
          "max": 1000000000,
          "unit": "Ω"
        },
        "r6": {
          "min": 0,
          "max": 1000000000,
          "unit": "Ω"
        },
        "r7": {
          "min": 0,
          "max": 1000000000,
          "unit": "Ω"
        },
        "r8": {
          "min": 0,
          "max": 1000000000,
          "unit": "Ω"
        },
        "numParts": {
          "min": 1,
          "max": 8,
          "unit": ""
        },
        "componentType": {
          "min": 0,
          "max": 2,
          "unit": ""
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "r1": 1000,
      "r2": 1000,
      "r3": 0,
      "r4": 0,
      "r5": 0,
      "r6": 0,
      "r7": 0,
      "r8": 0,
      "numParts": 4,
      "componentType": 0
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "r1"
      ],
      "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 pageSeries / Parallel Resistor, Capacitor & Inductor Calculator, at these values