NTC Thermistor Beta Value: Inputs and Datasheet Checks
This page is a practical guide to selecting and checking an NTC thermistor beta value. It does not contain an interactive calculator. For an OEM design, the beta value must be tied to the sensor’s stated temperature interval and resistance–temperature (R/T) data; a single number cannot guarantee accuracy across every temperature.
What the beta value describes
An NTC thermistor’s resistance generally falls as temperature rises. The beta value (B, in kelvins) is a two-point approximation of the curve over a specified interval, for example B25/50. The interval matters: values calculated over different temperature pairs can differ. Beta is not one of the three Steinhart–Hart coefficients, and it should not be presented as a universal material constant.
Data to collect before calculating
- Part number and nominal resistance, such as R25, with its tolerance.
- The two resistance readings and their paired temperatures, measured with a traceable reference where possible.
- The supplier’s beta definition and interval (such as B25/50), tolerance, and full R/T table or curve.
- Measurement conditions, including excitation current, settling time, mounting and lead configuration.
If the supplier publishes the required interval and tolerance, use those specified values for design review. Do not substitute a beta calculated from arbitrary points and assume it represents the complete operating range.
Two-point beta calculation
For each measured pair (R1, T1) and (R2, T2), convert both temperatures to kelvins and calculate:
B = ln(R1/R2) ÷ (1/T1 − 1/T2)
Use the natural logarithm and keep each resistance paired with its own temperature. As an illustrative example, 10 kΩ at 25°C and 3.59 kΩ at 50°C produce a beta value of approximately 3,946 K for that interval. These example values are not a Starlight product specification. For the derivation and a separate worked calculation, see our NTC beta calculation guide.
Using beta in a temperature estimate
When a beta approximation is appropriate, estimate temperature from measured resistance with a stated reference pair (R0, T0):
T = 1 ÷ [1/T0 + ln(R/R0)/B]
All temperatures in this equation must be kelvins (T(K) = t(°C) + 273.15). Implement the exact coefficient and unit conventions from the supplier data. Where the operating span is broad or the error budget is tight, use the part-specific R/T table or supplier-approved fit rather than extrapolating one beta value. Our NTC beta model guide explains the equation and its limits.
Validate the complete measurement chain
Check resistance and beta tolerances against the required system error budget. Then evaluate the divider or current source, ADC resolution, reference stability, lead resistance where relevant, self-heating and thermal contact. Validate the finished assembly at representative points across the operating span against an independent reference; document the sensor lot, curve, calibration results and firmware conversion.
For OEM selection, share the target temperature range, nominal resistance, required R/T curve and tolerance, probe construction, cable and connector, mounting constraints and annual quantity. See the NTC circuit design guide, browse the NTC sensor range, or request an OEM quotation.
Technical reference: TDK, NTC Thermistor General Technical Information.
