Beta equation: R(T) = R₀ × exp(β×(1/T − 1/T₀)), with T and T₀ in Kelvin (K = °C + 273.15). Reverse: T = 1 ÷ (1/T₀ + (1/β)×ln(R/R₀)). This is the standard simplified NTC model used on most datasheets — accurate over a moderate range around T₀; for wide-range precision work, manufacturers publish a more complex Steinhart-Hart 3-coefficient model instead. β and R₀ are printed on your specific thermistor's datasheet.