NTC Thermistor Calculator (Beta Equation)
Temperature from the resistance of an NTC thermistor, and its resistance at any temperature, using the B (beta) value from the datasheet.
Results
Temperature from the measured resistance
41.46
°C
Resistance at that temperature
3.5882
kΩ
The dashed line marks the value you entered.
What this tool does
An NTC thermistor's resistance falls steeply as it warms — a 10 kΩ part with B = 3950 drops to about 3.6 kΩ at 50 °C and to under 1 kΩ near 100 °C, as the curve shows. The beta equation is a two-parameter fit and is typically good to a fraction of a degree within some tens of degrees of 25 °C; for wide ranges the three-parameter Steinhart–Hart equation does better. Keep the measuring current small, because self-heating makes the thermistor read warm.
Formula
R(T) = R₂₅ × e^(B(1/T − 1/298.15)) · 1/T = 1/298.15 + ln(R ÷ R₂₅) ÷ B
Variables
| Symbol | Meaning | Unit |
|---|---|---|
r0 | Resistance at 25 °C (R25) | kΩ |
bt | B constant (beta) | K |
rm | Measured resistance | kΩ |
tq | Temperature at which you want the resistance | °C |
T | Temperature from the measured resistance | °C |
R | Resistance at that temperature | kΩ |
Worked example
- Resistance at 25 °C (R25)10 kΩ
- B constant (beta)3950 K
- Measured resistance5 kΩ
- Temperature at which you want the resistance50 °C
- Temperature from the measured resistance41.46 °C
- Resistance at that temperature3.5882 kΩ
Limitations
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.