Documentation sections

Wheatstone Bridge Calculator

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

Slug wheatstone-bridge. Calculate Wheatstone bridge output voltage, balance condition, and mV/V sensitivity. Design circuits for strain gauges, RTDs, and load cells.

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 wheatstone-bridge
Name	Unit	Range	Default	Description
vinnumber	V	0.1 … 30	5	Bridge excitation supply voltage
r1number	Ω	at least 1	1000	Bridge resistor R1 (top-left arm)
r2number	Ω	at least 1	1000	Bridge resistor R2 (top-right arm)
r3number	Ω	at least 1	1000	Bridge resistor R3 (bottom-left arm, often the sensor)
r4number	Ω	at least 1	1000	Bridge resistor R4 (bottom-right arm)
frontGainnumber	V/V	0.01 … 100000	6	The gain between the bridge output and the ADC. A gain of 6 brings the bridge's 0.5 V output with R3 at 1.5 kΩ to 3 V.
adcRefnumber	V	0.1 … 50	3.3	The ADC full scale. The ADC is unipolar: a negative bridge output reads 0.
adcBitsnumber	bit	1 … 24	12	ADC resolution in bits

Outputs

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

Outputs of wheatstone-bridge
Field	Unit	Description
voutheadline	V	Differential output voltage of the bridge
voutMv	mV	Differential output voltage in millivolts
balance	none	Balance indicator: 0 = perfectly balanced (R1/R3 = R2/R4)
sensitivity	mV/V	Bridge sensitivity: output mV per V of excitation
amplifiedVoltage	V	The bridge output times the amplifier gain
adcCode	none	The code an ideal ADC reads: floor(V_amp / V_ref × 2^N), 0 below zero
resolution	Ω/LSB	The change in R3 one ADC step spans at this point

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": "wheatstone-bridge",
    "inputs": {
      "vin": 5,
      "r1": 1000,
      "r2": 1000,
      "r3": 1000,
      "r4": 1000,
      "frontGain": 6,
      "adcRef": 3.3,
      "adcBits": 12
    }
  }'

import rftools

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

result = client.calculate("wheatstone-bridge", {
    "vin": 5,
    "r1": 1000,
    "r2": 1000,
    "r3": 1000,
    "r4": 1000,
    "frontGain": 6,
    "adcRef": 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": "wheatstone-bridge",
    "inputs": {
      "vin": 5,
      "r1": 1000,
      "r2": 1000,
      "r3": 1000,
      "r4": 1000,
      "frontGain": 6,
      "adcRef": 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": "wheatstone-bridge",
	  "inputs": {
	    "vin": 5,
	    "r1": 1000,
	    "r2": 1000,
	    "r3": 1000,
	    "r4": 1000,
	    "frontGain": 6,
	    "adcRef": 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": "wheatstone-bridge",
  "values": {
    "vout": 0,
    "voutMv": 0,
    "balance": 0,
    "sensitivity": 0,
    "amplifiedVoltage": 0,
    "adcCode": 0,
    "resolution": 0.107421875
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:wheatstone-bridge",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "vin": {
          "min": 0.1,
          "max": 30,
          "unit": "V"
        },
        "r1": {
          "min": 1,
          "max": null,
          "unit": "Ω"
        },
        "r2": {
          "min": 1,
          "max": null,
          "unit": "Ω"
        },
        "r3": {
          "min": 1,
          "max": null,
          "unit": "Ω"
        },
        "r4": {
          "min": 1,
          "max": null,
          "unit": "Ω"
        },
        "frontGain": {
          "min": 0.01,
          "max": 100000,
          "unit": "V/V"
        },
        "adcRef": {
          "min": 0.1,
          "max": 50,
          "unit": "V"
        },
        "adcBits": {
          "min": 1,
          "max": 24,
          "unit": "bit"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "vin": 5,
      "r1": 1000,
      "r2": 1000,
      "r3": 1000,
      "r4": 1000,
      "frontGain": 6,
      "adcRef": 3.3,
      "adcBits": 12
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "vin"
      ],
      "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 pageWheatstone Bridge Calculator, at these values