NTC thermistor beta resistance calculator
A 10 kΩ NTC with a beta of 3950 K, rated at 25 °C, drops below 4 kΩ at 50 °C. Enter the nominal resistance, beta and the temperature you need to get the resistance in ohms, for divider and sensor planning. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Nominal resistance ohms
- 10,000
- Beta kelvin
- 3,950
- Temperature c
- 50
- Reference temperature c
- 25
- Resistance ohms
- 3,588.18258193
- Temperature kelvin
- 323.15
- Reference temperature kelvin
- 298.15
- Exponent
- -1.0249392633
This NTC thermistor beta resistance calculator estimates resistance at a chosen temperature from the part's nominal resistance, beta parameter, and reference temperature. It applies the standard single-beta equation with temperatures converted to kelvins, returning the resistance in ohms plus useful intermediate values. It is designed for quick component checks, sensor-interface planning, and reproducible engineering calculations where the beta model is an appropriate practical approximation rather than a full calibration curve.
Enter values from the thermistor datasheet
Start with the nominal resistance, usually written as R25 when the reference temperature is 25 degrees Celsius. A common device is described as 10 kΩ at 25 degrees Celsius, so its nominal resistance input is 10000 ohms and its reference temperature is 25. Next enter the beta parameter in kelvins.
Datasheets may print this as B, β, B25/50, or B25/85. The stated temperature interval matters because beta is an approximation fitted over that interval; choose the beta value whose interval best covers your intended operating region. Finally, enter the temperature where resistance is needed.
Both temperature fields use degrees Celsius for convenient entry, while the calculator converts them to absolute temperature internally. Every required value must be finite, resistance and beta must be positive, and temperatures must remain above absolute zero. Keep units consistent: do not enter 10 for a 10 kΩ part unless you deliberately want the result expressed from a nominal value of 10 ohms.
The returned resistance is always labeled in ohms.
Understand the beta equation and result
The calculation uses R(T) = R0 × exp[B × (1/T − 1/T0)]. In that expression, R0 is nominal resistance, B is the beta value in kelvins, T is the requested absolute temperature, and T0 is the absolute reference temperature. Celsius temperatures cannot be inserted directly into reciprocal temperature terms, so the calculator adds 273.15 before evaluating the formula.
For an NTC device with a positive beta value, resistance falls as temperature rises: above the reference temperature the exponent becomes negative, while below the reference it becomes positive. At the exact reference temperature, the reciprocal-temperature difference is zero, exp(0) is one, and the result equals nominal resistance. Extremely large or small combinations that overflow ordinary finite arithmetic are rejected instead of returning an unusable infinity or zero.
Know when the approximation is suitable
The beta model is useful for estimating behavior, selecting a resistor-divider range, checking an analog-to-digital converter input, or building a compact lookup approximation. It does not capture every real thermistor characteristic. Beta can vary with temperature, component tolerance shifts the nominal resistance, self-heating raises bead temperature above ambient, and lead or contact resistance can matter at low resistance values.
For high-accuracy measurement across a broad range, use the manufacturer's resistance-versus-temperature table, Steinhart–Hart coefficients, or a calibration fitted to the individual sensor. Also distinguish resistance calculation from complete circuit analysis: this result does not account for supply voltage, divider topology, ADC reference, dissipation constant, thermal time constant, or allowable measurement current. Treat the output as the resistance predicted by the supplied beta model, not a guarantee for every physical sample.
When designing hardware, evaluate tolerance at the cold and hot limits and ensure measurement current does not cause significant self-heating. When implementing firmware, compare several values against the datasheet table before releasing coefficients.
What you can do with it
Size a sensor voltage divider
Estimate thermistor resistance at the hot and cold design points before choosing a fixed divider resistor and ADC range.
Check firmware calculations
Generate reference resistance values to compare with an embedded beta-equation implementation or a lookup table.
Compare thermistor candidates
Evaluate how nominal resistance and beta values affect resistance across a target operating temperature.
FAQ
What equation does the calculator use?
It uses R(T) = R0 × exp[B × (1/T − 1/T0)], with T and T0 converted to kelvins.
What should I use for the reference temperature?
Use the temperature associated with the datasheet's nominal resistance. It is commonly 25 degrees Celsius, which is the default.
Why does resistance decrease when temperature increases?
An NTC thermistor has a negative temperature coefficient. With a positive beta value, the beta equation therefore predicts lower resistance at higher temperature.
Can I enter resistance in kilohms?
The declared input and output unit is ohms. Convert kilohms to ohms before submitting, such as 10 kΩ to 10000 Ω.
Is the beta equation exact across the full temperature range?
No. It is a one-parameter approximation. Use a datasheet table, Steinhart–Hart coefficients, or calibration data when accuracy over a wide range is important.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/elec/ntc-thermistor-resistance \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"nominal_resistance_ohms":10000,"beta_kelvin":3950,"temperature_c":50}'const res = await fetch("https://api.kit.forhosting.com/elec/ntc-thermistor-resistance", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"nominal_resistance_ohms": 10000,
"beta_kelvin": 3950,
"temperature_c": 50
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/elec/ntc-thermistor-resistance",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"nominal_resistance_ohms": 10000,
"beta_kelvin": 3950,
"temperature_c": 50
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/elec/ntc-thermistor-resistance", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"nominal_resistance_ohms":10000,"beta_kelvin":3950,"temperature_c":50}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"nominal_resistance_ohms":10000,"beta_kelvin":3950,"temperature_c":50}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/elec/ntc-thermistor-resistance", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"nominal_resistance_ohms": 10000,
"beta_kelvin": 3950,
"temperature_c": 50
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "elec.ntc_thermistor_resistance",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Understand the beta equation and result
The response includes resistance_ohms, both converted kelvin temperatures, and the dimensionless exponent. Those intermediate fields make it easier to audit a spreadsheet, firmware constant, or hand calculation.
Know when the approximation is suitable
One API request is priced at $0.002, and the same deterministic inputs always produce the same output.
Technical questions
How much does an API calculation cost?
Each request costs $0.002. The calculation is deterministic and uses no network service.