NTC Thermistor Calculator
Calculate resistance from temperature or temperature from resistance using the Beta model. ADC voltage divider output.
NTC Parameters
Voltage Divider (for ADC)
Results
R(T) = R₀ × e^(B × (1/T − 1/T₀))
NTC Thermistors Explained
An NTC (Negative Temperature Coefficient) thermistor is a resistor whose resistance decreases as temperature increases. The relationship is exponential, not linear: a 10kΩ NTC might measure 30kΩ at 0°C and 4kΩ at 50°C. The Beta equation R(T) = R₀ × e^(B×(1/T − 1/T₀)) models this behavior with reasonable accuracy over a typical range of −20°C to 120°C.
The Beta coefficient (B value) characterizes the steepness of the R-T curve. Common NTC thermistors have B values between 3000K and 4500K. A higher B means the resistance changes more sharply with temperature — better sensitivity but also more nonlinearity. For the most accurate readings, use a lookup table or the Steinhart-Hart equation (three coefficients) instead of the simplified Beta model.
To read an NTC with a microcontroller, connect it in a voltage divider with a fixed resistor. The ADC reads a voltage that depends on the thermistor's resistance. Choose the fixed resistor equal to R₀ (the resistance at the midpoint of your temperature range) for the best resolution. A 10kΩ NTC with a 10kΩ fixed resistor gives good sensitivity around room temperature.
Beta Equation
R(T) = R₀ × e^(B × (1/T − 1/T₀))Key Points
- NTC: resistance decreases with temperature (negative coefficient)
- PTC: resistance increases with temperature (positive coefficient)
- Beta equation accuracy: ±1°C over −20°C to 100°C range
- Use series resistor ≈ R₀ for best ADC resolution at midrange
Applications
- Temperature measurement with Arduino/ESP32
- HVAC and climate control systems
- Battery temperature monitoring
- Inrush current limiting (NTC power thermistors)
Steinhart-Hart equations
Steinhart-Hart equation (full):
1/T = A + B×ln(R) + C×(ln(R))³
Simplified β equation:
1/T = 1/T₀ + (1/β) × ln(R/R₀)
R = R₀ × exp(β × (1/T - 1/T₀))
Where: T in Kelvin, T₀ = 298.15K (25°C), R₀ = nominal resistance at 25°C
β = 3000–5000K for typical NTC thermistorsCommon NTC thermistor types
| Type | R at 25°C | β value | Temp Range | Application |
|---|---|---|---|---|
| NTC 10kΩ B3950 | 10kΩ | 3950K | -40–125°C | Arduino / hobby |
| NTC 10kΩ B3977 | 10kΩ | 3977K | -40–125°C | Automotive |
| NTC 10kΩ B4150 | 10kΩ | 4150K | 0–70°C | HVAC systems |
| NTC 100kΩ | 100kΩ | 4250K | -55–150°C | Medical, industrial |
| NTC 1kΩ | 1kΩ | 3750K | -20–120°C | Motor temperature |
| PT1000 (RTD) | 1000Ω | — | -200–850°C | Precision industrial |
Practical examples
Voltage divider: Vcc=5V, R_fixed=10kΩ.
At 0°C: R_NTC≈32kΩ → V_out = 1.19V (ADC: 244/1023). At 50°C: R_NTC≈3.6kΩ → V_out = 3.68V (ADC: 754/1023).
At 200°C (473K): R = 100k × exp(4250×(1/473 - 1/298)) = 2.18kΩ
Firmware lookup table covers 20–300°C for reliable PID control.
Design tip: Self-heating error — thermistor current should keep P < 1% of dissipation constant D. For 10kΩ NTC with D=1mW/°C: max I = √(0.01×0.001/10000) = 31µA → use high-impedance ADC input. Use shielded cable for runs > 30cm to avoid noise pickup. Interchangeable NTCs (1% tolerance, matched β) eliminate calibration in production.
Did you know? The word "thermistor" is a portmanteau of "thermal" and "resistor." NTC (Negative Temperature Coefficient) thermistors can change resistance by a factor of 10× or more over a 100 °C range — far more sensitive than metal RTDs — making them ideal for low-cost temperature sensing.