Documentation sections

Current Shunt Resistor

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

Slug current-shunt. Calculate shunt resistor voltage drop, power dissipation, amplifier output, and ADC resolution for current sensing circuits. 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 current-shunt
Name	Unit	Range	Default	Description
currentnumber	A	at least 0	10	Measured Current
shuntResistancenumber	mΩ	at least 0.001	10	Shunt Resistance
amplifierGainnumber	V/V	at least 1	20	INA219: 1–128×, INA240: 20–200×
adcVoltagenumber	V	at least 0.1	3.3	ADC Reference Voltage
adcBitsnumber	bit	1 … 24	12	ADC resolution in bits; the ADC code and the resolution output use this many bits

Outputs

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

Outputs of current-shunt
Field	Unit	Description
shuntVoltageheadline	mV	Shunt Voltage Drop
amplifiedVoltage	V	Amplified Voltage
powerDissipation	mW	Shunt Power Dissipation
adcResolutionCurrent	mA/LSB	ADC Resolution (12-bit)
adcCode	none	The code an ideal ADC reads: floor(V_amp / V_ref × 2^N)
resolution	A/LSB	The current one ADC step spans at the ADC resolution above

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": "current-shunt",
    "inputs": {
      "current": 10,
      "shuntResistance": 10,
      "amplifierGain": 20,
      "adcVoltage": 3.3,
      "adcBits": 12
    }
  }'

import rftools

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

result = client.calculate("current-shunt", {
    "current": 10,
    "shuntResistance": 10,
    "amplifierGain": 20,
    "adcVoltage": 3.3,
    "adcBits": 12,
})
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": "current-shunt",
    "inputs": {
      "current": 10,
      "shuntResistance": 10,
      "amplifierGain": 20,
      "adcVoltage": 3.3,
      "adcBits": 12
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "current-shunt",
	  "inputs": {
	    "current": 10,
	    "shuntResistance": 10,
	    "amplifierGain": 20,
	    "adcVoltage": 3.3,
	    "adcBits": 12
	  }
	}`)
	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": "current-shunt",
  "values": {
    "shuntVoltage": 100,
    "amplifiedVoltage": 2,
    "powerDissipation": 1000,
    "adcResolutionCurrent": 4.028320312499999,
    "adcCode": 2482,
    "resolution": 0.004028320312499999
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:current-shunt",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "current": {
          "min": 0,
          "max": null,
          "unit": "A"
        },
        "shuntResistance": {
          "min": 0.001,
          "max": null,
          "unit": "mΩ"
        },
        "amplifierGain": {
          "min": 1,
          "max": null,
          "unit": "V/V"
        },
        "adcVoltage": {
          "min": 0.1,
          "max": null,
          "unit": "V"
        },
        "adcBits": {
          "min": 1,
          "max": 24,
          "unit": "bit"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "current": 10,
      "shuntResistance": 10,
      "amplifierGain": 20,
      "adcVoltage": 3.3,
      "adcBits": 12
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "current"
      ],
      "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 pageCurrent Shunt Resistor, at these values