The NTC thermistor beta value (B value) summarizes the relationship between resistance and temperature over a defined pair of temperatures. It helps engineers compare a thermistor curve with the conversion method used by a controller, but it is not a complete accuracy specification by itself.
What the beta value describes
An NTC thermistor’s resistance decreases as temperature rises. A beta value expresses the slope of an approximate resistance-temperature relationship between two specified points. Datasheets may state values such as B25/50 or B25/85; the temperature interval matters, so values defined over different intervals should not be treated as interchangeable.
Beta equation and units
For the simplified beta model, resistance R at absolute temperature T can be estimated from a reference resistance Rref at temperature Tref:
R = Rref × exp[B × (1/T − 1/Tref)]
When resistance is known at two temperatures, the corresponding two-point beta value is:
B = ln(R1/R2) / (1/T1 − 1/T2)
- R1 and R2 are resistance values measured or specified at the two points.
- T1 and T2 are the corresponding absolute temperatures in kelvins.
- B is expressed in kelvins (K); use the same temperature-resistance pair that the datasheet or application requires.
Use the manufacturer’s stated curve and reference interval when implementing the conversion. A two-point beta model is an approximation over its defined range. For broader ranges or tighter system accuracy, compare the complete resistance-temperature table or the conversion method recommended in the thermistor documentation.
How to choose a thermistor for a measurement circuit
Match the sensor data to the electronics and operating conditions. Review the nominal resistance at its reference temperature, beta value and interval, resistance and beta tolerances, required temperature span, controller input circuit, and firmware lookup or conversion method. Also consider thermal contact, response requirements, measurement current and self-heating in the installed assembly.
For battery-management applications, the thermistor curve and controller conversion also need to suit the battery operating range. See our e-bike battery temperature monitoring guide for an application example.
A beta value alone does not establish measurement accuracy. The complete result also depends on component tolerances, the readout circuit, calibration, installation and the conversion used by the controller.
OEM selection checklist
- Provide the required resistance-temperature curve and reference temperatures.
- Identify the controller input, conversion method and required tolerance across the operating span.
- Specify probe or bead form, mounting, lead length, connector and environmental exposure.
- Describe calibration or verification conditions, sample quantity and production forecast.
For a quick calculation, use our NTC thermistor beta value calculator. You can also review the NTC thermistor range or send your curve and assembly requirements for an OEM review.
