Thermocouple temperature & voltage
Convert between temperature and thermoelectric voltage (mV) for type K, J, T, N, E, and B thermocouples, using the NIST ITS-90 reference functions.
Calculator
Thermocouple converter
The thermoelectric voltage is the meter reading for a junction at the shown temperature with the reference (cold) junction held at the temperature you entered. Set the reference junction to 0 °C (the default) to match standard thermocouple tables, or to your ambient/terminal temperature for cold-junction compensation.
Formulas used
E(t) = Σ cᵢ × tⁱ— voltage from temperature (t in °C, E in mV, 0 °C reference)Type K above 0 °C adds: + a₀ × e^(a₁ × (t - a₂)²)t = Σ dᵢ × Eⁱ— temperature from voltage (piecewise by voltage sub-range)V_measured = E(t_hot) - E(t_ref)— reference-junction compensation (law of intermediate temperatures)°F = °C × 9/5 + 32
Coefficients are the NIST ITS-90 thermocouple reference functions and inverse functions. Inverse (voltage→temperature) functions carry NIST's stated tolerance of roughly ±0.05 °C.
Frequently asked questions
How is thermocouple voltage related to temperature?
Thermocouple output is a nonlinear function of temperature defined by the NIST ITS-90 reference functions, expressed relative to a 0 °C reference junction.
What is cold-junction (reference-junction) compensation?
Thermocouple tables assume the reference junction is at 0 °C. If it is at another temperature, add the equivalent reference-junction voltage before converting to temperature.
Which thermocouple types does this calculator support?
Types K, J, T, N, E, and B, using the ITS-90 reference functions.