Thermocouple Reference Calculator
Convert between temperature and thermocouple voltage for types K, J, T, E, R, S, B, N. Includes cold junction compensation and sensitivity (µV/°C) for each type.
How to Use
- Pick the thermocouple type (K is most common).
- Enter either temperature OR voltage to convert.
- Set cold-junction (reference) temperature — typically 0°C for ice-bath or room temperature for electronic CJC.
- Sensitivity tells you µV per °C at the measured temperature.
Show Work
Thermocouple Types
| Type | Metals | Range (°C) | Sensitivity | Use |
|---|---|---|---|---|
| K | Chromel / Alumel | −200 to 1260 | ~41 µV/°C | Universal default |
| J | Iron / Constantan | −210 to 760 | ~52 µV/°C | Legacy US industry |
| T | Copper / Constantan | −270 to 400 | ~43 µV/°C | Cryogenics / low-temp |
| E | Chromel / Constantan | −270 to 1000 | ~68 µV/°C | High sensitivity, low noise |
| N | Nicrosil / Nisil | −270 to 1300 | ~39 µV/°C | High-temp, drift-resistant |
| R/S | Pt-Rh / Pt | 0 to 1768 | ~10 µV/°C | High-temp precision |
| B | Pt-30Rh / Pt-6Rh | 250 to 1820 | ~8 µV/°C | Very high temp only |
Formulas
History of the Thermocouple
Thomas Johann Seebeck, an Estonian-German physicist, discovered in 1821 that a closed circuit of two dissimilar metals generates a continuous current when one junction is at a different temperature than the other. Seebeck originally attributed the effect to magnetism (he called it "thermomagnetism"), but Hans Christian Ørsted correctly identified it as a thermoelectric phenomenon — now the Seebeck effect. Its inverse, the Peltier effect (current produces cooling or heating), was discovered by Jean Charles Peltier in 1834.
Standardization of thermocouple types came in waves. Platinum-based Types R and S were calibrated to the International Temperature Scale in 1927 — still the reference standards for high-temperature calibration. Base-metal types K (chromel-alumel), J (iron-constantan), and T (copper-constantan) were standardized by ANSI and ASTM in the 1960s and remain the workhorse types for industrial and commercial use. Type N (nicrosil-nisil) was developed in the 1980s to solve drift problems with Type K at high temperatures.
NIST publishes polynomial approximations (ITS-90 standard) that characterize each type\'s V-T curve to better than ±0.1 °C over its rated range. Modern thermocouple signal-conditioning ICs (Maxim MAX31855, Analog Devices AD594) embed these polynomials plus a cold-junction sensor and amplifier into a single chip, producing a linear digital or analog output ready for an ADC. The 1821 discovery remains one of the oldest still-commercialized electrical phenomena.
About This Calculator
Pick a thermocouple type (K for general use, T for cryogenics, R/S/B for high-temp precision). Choose whether to convert temperature → voltage or voltage → temperature. Enter the value plus the cold-junction reference temperature (0 °C for an ice bath, 25 °C for room-temp electronic CJC). The tool applies the NIST polynomial for that type and returns the conversion plus local sensitivity in µV/°C.
Important: the raw thermocouple voltage measures the temperature difference between the hot junction and your measurement device\'s terminals. If your terminals aren\'t at 0 °C, you must add the voltage equivalent of the terminal temperature to the measurement — this is cold-junction compensation. Electronic CJC chips do this automatically; for bench measurements with a multimeter, use an ice-bath reference or record the ambient and correct afterward. Everything runs client-side.
Frequently Asked Questions
What is a thermocouple?
Two dissimilar metal wires joined at one end. The junction generates a voltage proportional to the temperature difference between the junction and a reference (cold) junction. It\'s the Seebeck effect — self-powered, no excitation needed.
Which type should I use?
Type K is the universal workhorse (−200°C to +1260°C, good accuracy). Type J is common in older US industry (−210 to +760°C). Type T for low temps and cryogenics. Types R/S/B for high-temp (up to 1800°C) precision — but expensive (platinum).
What is cold junction compensation?
The thermocouple measures ΔT from its tip to the measurement device\'s terminals. If the terminals aren\'t at 0°C, you must add the equivalent voltage to correct. Electronic CJC uses a second temperature sensor at the terminals.
Are thermocouples linear?
No. The voltage-temperature relationship is highly nonlinear over wide ranges. Linear approximation works within ±50°C of a given point; wider ranges need polynomial (NIST tables) or lookup tables. Most signal conditioners include these corrections.
Common Use Cases
Kiln / Furnace
Type K at 1000°C outputs 41.3mV. Transmitter scales to 4-20mA for process control.
Oven / BBQ Monitor
Type K up to 300°C, common in consumer grills. 12mV at 300°C with 0°C cold junction.
Cryogenic Sensing
Type T for liquid nitrogen (−196°C), where J/K lose accuracy. Typical output: −5.6mV.
Reflow Oven
PCB reflow curves need ±2°C accuracy around 230-250°C — Type K at ±0.75% is marginal; use Type T or a resistive RTD.
HVAC / Automotive
Exhaust gas temperature: Type K rated to ~1000°C, survives combustion byproducts better than RTDs.
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