NTC Thermistor Calculator (Beta Equation)
By Santaji GadepatilinUpdated October 28, 2026
An NTC thermistor's resistance falls sharply as it warms, making it a cheap and sensitive temperature sensor. The beta equation converts between resistance and temperature using the R25 and B values from the datasheet. This NTC thermistor calculator works both ways — see NTC and PTC thermistor working and thermistor vs thermocouple.
How to use the NTC thermistor calculator
Enter the thermistor’s R25 and beta value from the datasheet, then a temperature to get its resistance — or enter a measured resistance and press × on Temperature to read the temperature. The sensitivity shows how much resistance changes per °C at that point.
NTC beta equation
RT = R₂₅ × eB (1/T − 1/298.15) · T = 1 ÷ [1/298.15 + ln(R/R₂₅) ÷ B]
T is in kelvin (°C + 273.15).
10 kΩ, B = 3950 thermistor
| Temperature | Resistance | Sensitivity |
|---|---|---|
| -20 °C | 105.38 kΩ | -6.16 %/°C |
| 0 °C | 33.62 kΩ | -5.29 %/°C |
| 10 °C | 20.17 kΩ | -4.93 %/°C |
| 25 °C | 10.00 kΩ | -4.44 %/°C |
| 40 °C | 5.30 kΩ | -4.03 %/°C |
| 60 °C | 2.49 kΩ | -3.56 %/°C |
| 80 °C | 1.27 kΩ | -3.17 %/°C |
| 100 °C | 0.70 kΩ | -2.84 %/°C |
| 125 °C | 0.36 kΩ | -2.49 %/°C |
Reading a thermistor with an ADC
Place the thermistor in a voltage divider with a fixed resistor equal to R25. The divider output is most linear and sensitive around 25 °C. Keep the measuring current low (under about 100 µA for 10 kΩ) to avoid self-heating.
NTC vs Pt100
| NTC thermistor | Pt100 RTD | |
|---|---|---|
| Sensitivity | about −4%/°C | +0.39%/°C |
| Range | −40 to 150 °C typical | −200 to 600 °C+ |
| Linearity | Strongly non-linear | Nearly linear |
| Cost | Very low | Higher |
| Interchangeability | ±0.2–1 °C | Class A/B standards |
Frequently asked questions
What is the thermistor beta equation?
R = R25 × exp[B × (1/T − 1/298.15)], with T in kelvin. It is accurate to about ±1 °C over a range of 50–100 °C around 25 °C.
How do I find temperature from resistance?
Enter the measured resistance and press × on Temperature. The calculator solves T = 1 ÷ (1/298.15 + ln(R/R25) ÷ B) − 273.15.
What is a 10k 3950 thermistor?
A thermistor with 10 kΩ at 25 °C and a beta value of 3,950 K — one of the most common types for 3D printers, appliances and HVAC.
When should I use the Steinhart–Hart equation instead?
For wide temperature ranges or better than ±0.5 °C accuracy, use the three-coefficient Steinhart–Hart equation or the manufacturer's R–T table.