NTC Thermistor Calculator

Convert a thermistor resistance into a temperature using the B parameter equation. Works for any NTC where you know the nominal resistance and B value.

Nominal resistance at 25 C (ohms)

B value

Measured resistance (ohms)

Temperature --

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The formula

1/T = 1/T0 + (1/B) x ln(R / R0)

T, T0 in kelvin.  T0 = 298.15 K (25 C)
R0 = nominal resistance at 25 C
B  = beta value, e.g. 3950

How it works

An NTC drops in resistance as it warms, steeply and not in a straight line. The B parameter equation is the usual way to turn one into the other, and it is accurate to a degree or so across a normal room to boiling range.

A 10K B3950 thermistor reads 10 kOhm at 25 C, roughly 3.9 kOhm at 50 C and about 1.2 kOhm at 85 C. If your reading is far outside that band, suspect the wiring before the maths.

Most circuits read a thermistor through a divider, so the resistance you feed in here is the one you calculated from the ADC reading, not the ADC reading itself.

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