Documentation sections

NTC Thermistor Temperature Calculator

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

Slug ntc-thermistor. Calculate temperature from NTC thermistor resistance using the Steinhart-Hart beta equation. Get Kelvin and Celsius outputs for sensor circuit design.

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 ntc-thermistor
Name	Unit	Range	Default	Description
resistancenumber	Ω	at least 0.1	10000	Measured thermistor resistance at unknown temperature
betanumber	K	100 … 10000	3950	Beta (B) coefficient of the thermistor, from datasheet. Typically 3000–4500 K.
T0number	°C	−55 … 200	25	Reference temperature at which R0 is specified (usually 25°C)
R0number	Ω	at least 0.1	10000	Thermistor resistance at reference temperature T0 (e.g. 10kΩ at 25°C)
fixedResistornumber	Ω	at least 1	10000	The divider's fixed resistor: from the reference to the ADC node when the NTC is on the low side, from the ADC node to ground when it is on the high side
adcRefnumber	V	0.1 … 50	3.3	The voltage across the divider, which is also the ADC full scale (ratiometric)
adcBitsnumber	bit	1 … 24	12	ADC resolution in bits
ntcPositionnumber	none	any	0	Low side: the NTC from the ADC node to ground. High side: from the reference to the node.One of: 0 Low side · 1 High side

Outputs

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

Outputs of ntc-thermistor
Field	Unit	Description
temperatureheadline	°C	Calculated temperature in degrees Celsius
temperatureK	K	Calculated temperature in Kelvin
dividerVoltage	V	The voltage at the ADC node
adcCode	none	The code an ideal ADC reads: floor(V_out / V_ref × 2^N)
resolution	°C/LSB	The temperature 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": "ntc-thermistor",
    "inputs": {
      "resistance": 10000,
      "beta": 3950,
      "T0": 25,
      "R0": 10000,
      "fixedResistor": 10000,
      "adcRef": 3.3,
      "adcBits": 12,
      "ntcPosition": 0
    }
  }'

import rftools

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

result = client.calculate("ntc-thermistor", {
    "resistance": 10000,
    "beta": 3950,
    "T0": 25,
    "R0": 10000,
    "fixedResistor": 10000,
    "adcRef": 3.3,
    "adcBits": 12,
    "ntcPosition": 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": "ntc-thermistor",
    "inputs": {
      "resistance": 10000,
      "beta": 3950,
      "T0": 25,
      "R0": 10000,
      "fixedResistor": 10000,
      "adcRef": 3.3,
      "adcBits": 12,
      "ntcPosition": 0
    }
  }),
});
console.log(response.status, await response.json());

package main

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

func main() {
	body := []byte(`{
	  "slug": "ntc-thermistor",
	  "inputs": {
	    "resistance": 10000,
	    "beta": 3950,
	    "T0": 25,
	    "R0": 10000,
	    "fixedResistor": 10000,
	    "adcRef": 3.3,
	    "adcBits": 12,
	    "ntcPosition": 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": "ntc-thermistor",
  "values": {
    "temperature": 25,
    "temperatureK": 298.15,
    "dividerVoltage": 1.65,
    "adcCode": 2048,
    "resolution": 0.021977210863330692
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:ntc-thermistor",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "resistance": {
          "min": 0.1,
          "max": null,
          "unit": "Ω"
        },
        "beta": {
          "min": 100,
          "max": 10000,
          "unit": "K"
        },
        "T0": {
          "min": -55,
          "max": 200,
          "unit": "°C"
        },
        "R0": {
          "min": 0.1,
          "max": null,
          "unit": "Ω"
        },
        "fixedResistor": {
          "min": 1,
          "max": null,
          "unit": "Ω"
        },
        "adcRef": {
          "min": 0.1,
          "max": 50,
          "unit": "V"
        },
        "adcBits": {
          "min": 1,
          "max": 24,
          "unit": "bit"
        },
        "ntcPosition": {
          "min": null,
          "max": null,
          "unit": ""
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "resistance": 10000,
      "beta": 3950,
      "T0": 25,
      "R0": 10000,
      "fixedResistor": 10000,
      "adcRef": 3.3,
      "adcBits": 12,
      "ntcPosition": 0
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "resistance"
      ],
      "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 pageNTC Thermistor Temperature Calculator, at these values