Documentation sections

Ohm's Law Calculator

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

Slug ohms-law. Calculate voltage, current, resistance, and power using Ohm's Law. Enter any two values to solve for the remaining two quantities.

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 ohms-law
Name	Unit	Range	Default	Description
voltagenumber	V	0 … 1000000	5	Set to -1 to solve for this value
currentnumber	A	−1 … 1000000	-1	Set to -1 to solve for this value
resistancenumber	Ω	−1 … 1000000000000	1000	Set to -1 to solve for this value
powernumber	W	−1 … 1000000000000	-1	Set to -1 to solve for this value

Outputs

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

Outputs of ohms-law
Field	Unit	Description
voltage	V	Voltage
currentheadline	A	Current
resistance	Ω	Resistance
power	W	Power

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": "ohms-law",
    "inputs": {
      "voltage": 5,
      "current": -1,
      "resistance": 1000,
      "power": -1
    }
  }'

import rftools

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

result = client.calculate("ohms-law", {"voltage": 5, "current": -1, "resistance": 1000, "power": -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": "ohms-law",
    "inputs": {
      "voltage": 5,
      "current": -1,
      "resistance": 1000,
      "power": -1
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "ohms-law",
	  "inputs": {
	    "voltage": 5,
	    "current": -1,
	    "resistance": 1000,
	    "power": -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": "ohms-law",
  "values": {
    "voltage": 5,
    "current": 0.005,
    "resistance": 1000,
    "power": 0.025
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:ohms-law",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "voltage": {
          "min": 0,
          "max": 1000000,
          "unit": "V"
        },
        "current": {
          "min": -1,
          "max": 1000000,
          "unit": "A"
        },
        "resistance": {
          "min": -1,
          "max": 1000000000000,
          "unit": "Ω"
        },
        "power": {
          "min": -1,
          "max": 1000000000000,
          "unit": "W"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "voltage": 5,
      "current": -1,
      "resistance": 1000,
      "power": -1
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "voltage"
      ],
      "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 pageOhm's Law Calculator, at these values