Thermocouple Table and mV Calculator

This free thermocouple table tool lists the voltage a thermocouple produces at each temperature, and converts in both directions between millivolts and temperature for types K, J, T, E, N, R, S and B. It runs in your browser, with no sign-up needed. Use it to build a type K or type J thermocouple table, check a reading, or export a thermocouple chart for a design, quote or report. Results update as you type, so you can change the type, unit or reference temperature and see the new values straight away. It also works on a phone.

The data are the NIST ITS-90 reference functions.

How to use the Thermocouple Table

1. Choose the conversion mode: temperature → millivolts, or millivolts → temperature.
2. Select the thermocouple type, such as K, J, T, E, N, R, S or B.
3. Pick the unit, °C or °F.
4. Enter the reference (cold) junction temperature. Leave it empty to use 0 °C, the ice-point reference used in standard tables.
5. Type your value in the input field. The result updates as you type.
6. To build a full table, set the step and range for the chosen type. The table shows the voltage and temperature at each row.
7. Look at the curve drawing to see how voltage changes with temperature.
8. Open “How it was calculated” to see the formula and each step with your numbers.

Use Copy result to copy the result lines with a link. Copy link copies the page address, which stores every input, so opening it later restores the same calculation. Print / save as PDF prints the inputs, results, calculation steps and the date.

The presets show type K at 100 °C, a type K reading of 4.096 mV, type J at 200 °C and a 10 mV type K reading with the reference junction at 25 °C. Set the table step and range, then print the table with Print / save as PDF.

How do you convert thermocouple millivolts to temperature?

You cannot divide the millivolts by a fixed factor, because the voltage is not linear in temperature. The tool uses the full NIST ITS-90 polynomials and solves them numerically for the temperature. For example, a type K reading of 4.096 mV gives 99.994 °C.

What is the mV output of a type K thermocouple?

A type K thermocouple produces about 4.096 mV at 100 °C and about 20.644 mV at 500 °C, measured against a 0 °C reference. The output rises with temperature but not in a straight line. Enter any temperature in the tool to get its exact value.

What is cold junction compensation?

A thermocouple measures the difference between its hot junction and its reference (cold) junction, not the absolute temperature. The tool corrects for this with the formula measured voltage = E(t) − E(t_ref), where E is the reference function for the type. If your reference junction is at 25 °C, enter 25. For example, a type T reading of 3.5 mV with the reference at 25 °C gives 104.55 °C.

What are the thermocouple color codes?

In the US (ANSI MC96.1), the type K pair is yellow/red, type J is white/red, type T is blue/red, type E is purple/red and type N is orange/red. In US practice the red wire is always the negative leg. Under IEC 60584-3, the positive leg is green for K, black for J, brown for T, violet for E, pink for N, and orange for R and S, with a white negative leg. No IEC colour code is established for type B.

What is the difference between type K and type J?

Type K is a general-purpose thermocouple. Type J is typically used with older equipment and in reducing atmospheres. The two types produce different voltages at the same temperature. For instance, type J gives 10.779 mV at 200 °C (392 °F). Enter both types in the tool to compare their outputs at your working temperature.

Why is a thermocouple table referenced to 0 °C?

The ice point (0 °C) is a stable, easily reproduced reference that anyone can create. Tables set the reference at 0 °C so that every table uses the same baseline. Other reference temperatures are handled by adding or subtracting the reference function, as described above.

Sources

Checked October 2026:

• NIST ITS-90 Thermocouple Database (coefficients): all 8 types and 12,033 table points match within rounding
• WIKA international thermocouple colour chart and TC Direct colour codes for ANSI MC96.1 and IEC 60584-3 colours (none established for type B)

For estimation; verify critical designs against the applicable standard.

Worked examples

Calculated by the tool above with these values.

Frequently asked questions

Is a thermocouple chart the same as a thermocouple table?

They show the same data, voltage against temperature for one thermocouple type. The tool builds a table with an adjustable step and range, and it also draws the curve, so you can use either form.

Can I use the results in commercial work?

Yes. Results may be used in designs, quotes, documentation and reports without attribution.

Do I need an account or to upload anything?

No. The tool is free, requires no sign-up, and runs entirely in your browser, so nothing is uploaded.

What does the tool warn about for type B?

Type B produces almost no voltage at low temperatures: about 0.002 mV at 50 °C and 0.033 mV at 100 °C in the NIST table. The tool shows a warning when the type B hot junction is below 100 °C.

Which thermocouple type has the highest output?

Type E produces the most voltage per degree of the common types (21.04 mV at 300 °C), which is why it is used where resolution matters.

Can I use the table in °F?

Yes. Choose °F as the temperature unit; type J at 392 °F gives 10.779 mV.

Why does my thermocouple read wrong with copper extension wire?

Every junction of different metals makes its own voltage; use extension wire of the matching thermocouple type so the reference junction is at the instrument, where it is compensated.

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