Use a manufacturer’s resistance-temperature (R/T) data to convert an NTC thermistor reading into temperature. A basic Excel worksheet can implement the Beta equation when the sensor’s nominal resistance, reference temperature and Beta value are known. The equation is an approximation: do not treat a generic spreadsheet as a universal calculator for every thermistor.
Inputs to collect from the datasheet
- R₀: nominal resistance at the reference temperature.
- T₀: the reference temperature, converted to kelvin for calculation.
- B: Beta value in kelvin, with its specified temperature interval.
- R: measured thermistor resistance, expressed in the same unit as R₀.
Do not assume that “10k” or another nominal resistance identifies the full curve. Use the datasheet for the exact part. Our NTC beta value guide explains why the interval matters.
Beta equation for Excel
The two-point Beta model is: 1/T = 1/T₀ + (1/B) × ln(R/R₀), where T and T₀ are absolute temperatures in kelvin. To display the calculated result in Celsius, subtract 273.15 after calculating T.
For example, put R₀ in cell B2 (ohms), T₀ in B3 (°C), B in B4 (K), and measured R in B5 (ohms). In B6, use:
=1/(1/(B3+273.15)+LN(B5/B2)/B4)-273.15
The cell references are an example worksheet layout. Replace the values with the exact sensor datasheet values and the measured resistance.
Estimating Beta from two datasheet points
If the manufacturer provides two resistance-temperature points, the interval Beta can be calculated as B = ln(R₁/R₂) / (1/T₁ − 1/T₂), with T₁ and T₂ in kelvin. A calculated Beta describes that interval; it should not be assumed to stay identical across a broad temperature range.
Know the model’s limits
The Beta equation is a simplified curve model. Its error can increase away from the temperature interval used to define B. For wider ranges or tighter accuracy requirements, use the manufacturer’s full R/T table, an appropriate interpolation method or a specified Steinhart–Hart model, then validate against the application’s measurement requirements. Also account for resistance and Beta tolerances, measurement current and self-heating.
OEM design checklist
- Confirm the exact part number, R₀, reference temperature and B interval.
- Compare calculated temperatures with the datasheet R/T table across the intended range.
- Document controller input, measurement current, wiring and calibration requirements.
- Specify the probe or bead construction, mounting, cable and environmental exposure.
Browse the NTC thermistor range or send your curve and application requirements for an OEM review.
Technical reference
TDK Electronics’ NTC thermistor technical information describes the Beta model and the resistance-temperature relationship.
