Please enter all required numeric values.
Formulas & Mathematical Logic
Step 1: Resistance ratio: lr = ln(R / Rt). This compares measured thermistor resistance with reference resistance.
Step 2: Kelvin temperature: T(K) = 1 / (A + B × lr + C × lr² + D × lr³).
Step 3: Celsius conversion: T(°C) = T(K) - 273.15.
Practical meaning: the formula converts the nonlinear NTC thermistor resistance curve into temperature.
Step-by-Step Example
Example values: A = 0.003354016, B = 0.000256985, C = 0.000002620, D = 0.00000006383, Rt = 10000 Ω, R = 10000 Ω.
Resistance ratio: lr = ln(10000 / 10000) = 0.
T(K) = 1 / (A + B × 0 + C × 0² + D × 0³).
T(K) = 1 / 0.003354016 = about 298.15 K.
T(°C) = 298.15 - 273.15 = about 25 °C.
Practical meaning: when measured resistance equals a 10k reference thermistor value, the temperature is often near 25 °C depending on coefficients.
About This Calculator
Turn a nonlinear NTC thermistor resistance reading into a usable temperature value.
This CalcBoy calculator uses the Steinhart-Hart equation to estimate temperature from thermistor resistance and curve coefficients.
The Steinhart-Hart Thermistor Calculator is useful when working with NTC temperature sensors, voltage divider circuits, ADC measurements, battery temperature monitoring, HVAC controls, 3D printer thermistors and embedded temperature sensing. NTC thermistors are popular because they are small, low-cost and sensitive, but their resistance does not change linearly with temperature. That is why a curve-fit equation is needed.
Best UseNTC thermistors, temperature sensing, ADC projects, Arduino circuits and sensor calibration.
Key InputsA, B, C, D coefficients, reference resistance and measured thermistor resistance.
Design BenefitConvert resistance readings into temperature without manually solving the nonlinear curve.
Practical ReminderAccuracy depends on real thermistor coefficients, resistor tolerance and ADC calibration.
In many circuits, the thermistor is connected as a voltage divider with a fixed resistor. The microcontroller reads output voltage, then the circuit converts that voltage into thermistor resistance. After resistance is known, the Steinhart-Hart equation converts it into temperature. This calculator handles the resistance-to-temperature part.
Quick tip: for best accuracy, use coefficients from the thermistor datasheet or calculate them from measured calibration points instead of guessing generic values.
Real temperature measurement also depends on self-heating, lead resistance, ADC reference voltage, fixed resistor tolerance, thermal contact, sensor placement and airflow. For precision systems, calibrate the thermistor at known temperatures and use stable resistors in the voltage divider. For basic electronics projects, this calculator gives a fast way to check whether a measured resistance value matches the expected temperature range.
Frequently Asked Questions
What is the Steinhart-Hart equation?
It is a curve-fit equation used to convert thermistor resistance into temperature over a nonlinear resistance-temperature curve.
What is an NTC thermistor?
An NTC thermistor is a temperature sensor whose resistance decreases as temperature increases.
Where do I get A, B, C and D coefficients?
Use the thermistor datasheet, manufacturer curve table or calibration data measured at known temperatures.
Why do I need Rt?
Rt is the reference resistance used in the resistance ratio term ln(R / Rt).
Can I use this with Arduino?
Yes. First calculate thermistor resistance from the ADC voltage divider, then enter the resistance into this calculator.
Does this calculator convert voltage directly?
No. It calculates temperature from resistance. Use a voltage divider equation first to convert measured voltage into resistance.