Temperature ↔ EMF
Convert Type K Temperature and Millivolts
Nominal NIST ITS-90 conversion with an explicit cold-junction temperature.
Static example: a nominal Type K junction at 100°C produces 4.096 mV relative to a 0°C reference junction.
Show calculation
- Hot-junction nominal EMF
- 4.096 mV / 4096 µV
- Reference-junction nominal EMF
- 0.000 mV / 0 µV
- Junction operation
- 4.096 mV − 0.000 mV = 4.096 mV
- Function range
- Direct nonnegative polynomial plus exponential correction
- Rounding
- Full precision is retained internally; displayed values are rounded deliberately.
Nominal reference values
The reference function does not guarantee probe or measurement-system accuracy. Sensor tolerance, cold-junction sensing, wiring, connectors, thermal gradients, drift, noise, and instrument error still apply.
Limited calculated checkpoints
Type K Thermocouple Reference Table
Nominal values relative to a 0°C reference junction.
Use the converter for exact intermediate values. The highlighted row is the nearest currently displayed checkpoint; equal-distance ties use the lower temperature.
No displayed checkpoint matches this filter. Clear the filter or use the converter for an exact value within the supported range.
The 100°C checkpoint corresponds to the default example.
Scroll horizontally to view additional columns and vertically to view additional rows. Column headers remain visible while scrolling.
| Temperature | Nominal Type K output at 0°C reference | Derived | Scope | ||
|---|---|---|---|---|---|
| −270 | −454 | −6.458 | −6458 | 0.7 | Forward only below −200°C |
| −250 | −418 | −6.404 | −6404 | 4.9 | Forward only below −200°C |
| −200 | −328 | −5.891 | −5891 | 15.3 | Inverse supported |
| −150 | −238 | −4.913 | −4913 | 23.6 | Inverse supported |
| −100 | −148 | −3.554 | −3554 | 30.5 | Inverse supported |
| −50 | −58 | −1.889 | −1889 | 35.8 | Inverse supported |
| 0 | 32 | 0.000 | 0 | 39.5 | Inverse supported |
| 50 | 122 | 2.023 | 2023 | 41.2 | Inverse supported |
| 100 | 212 | 4.096 | 4096 | 41.4 | Inverse supported |
| 150 | 302 | 6.138 | 6138 | 40.3 | Inverse supported |
| 200 | 392 | 8.138 | 8138 | 40.0 | Inverse supported |
| 250 | 482 | 10.153 | 10153 | 40.7 | Inverse supported |
| 300 | 572 | 12.209 | 12209 | 41.4 | Inverse supported |
| 350 | 662 | 14.293 | 14293 | 41.9 | Inverse supported |
| 400 | 752 | 16.397 | 16397 | 42.2 | Inverse supported |
| 450 | 842 | 18.516 | 18516 | 42.5 | Inverse supported |
| 500 | 932 | 20.644 | 20644 | 42.6 | Inverse supported |
| 550 | 1022 | 22.776 | 22776 | 42.6 | Inverse supported |
| 600 | 1112 | 24.905 | 24905 | 42.5 | Inverse supported |
| 650 | 1202 | 27.025 | 27025 | 42.3 | Inverse supported |
| 700 | 1292 | 29.129 | 29129 | 41.9 | Inverse supported |
| 750 | 1382 | 31.213 | 31213 | 41.5 | Inverse supported |
| 800 | 1472 | 33.275 | 33275 | 41.0 | Inverse supported |
| 850 | 1562 | 35.313 | 35313 | 40.5 | Inverse supported |
| 900 | 1652 | 37.326 | 37326 | 40.0 | Inverse supported |
| 950 | 1742 | 39.314 | 39314 | 39.5 | Inverse supported |
| 1000 | 1832 | 41.276 | 41276 | 39.0 | Inverse supported |
| 1050 | 1922 | 43.211 | 43211 | 38.4 | Inverse supported |
| 1100 | 2012 | 45.119 | 45119 | 37.9 | Inverse supported |
| 1150 | 2102 | 46.995 | 46995 | 37.2 | Inverse supported |
| 1200 | 2192 | 48.838 | 48838 | 36.5 | Inverse supported |
| 1250 | 2282 | 50.644 | 50644 | 35.7 | Inverse supported |
| 1300 | 2372 | 52.410 | 52410 | 34.9 | Inverse supported |
| 1350 | 2462 | 54.138 | 54138 | 34.2 | Inverse supported |
| 1372 | 2501.6 | 54.886 | 54886 | 33.9 | Upper endpoint |
This is a limited, independently calculated checkpoint set—not the complete NIST reference table. It does not state the tolerance or usable limit of a particular probe, sheath, wire, connector, instrument, or installation.
How to Read and Use the Type K Chart
Look up a nominal value
- Find the hot-junction temperature in the °C or °F column.
- Read the nominal EMF in mV or µV. Table values assume a 0°C reference junction.
- Use the converter when the exact temperature falls between displayed checkpoints or when the reference junction is not 0°C.
Why the reference junction matters
A thermocouple responds to the temperature difference represented by two junction EMFs. For a hot junction at Th and reference junction at Tr, the measured voltage is:
For reverse conversion, add the reference-junction EMF, apply the correct bounded inverse polynomial, and refine against the direct reference function to avoid carrying the inverse approximation error into the displayed result.
Range and reference conditions
- Thermoelements
- Nominal nickel-chromium versus nickel-aluminum Type K materials.
- Forward function
- −270°C to 1372°C on ITS-90.
- Inverse function
- Approximately −200°C to 1372°C after cold-junction compensation; the published inverse polynomial supplies the initial estimate.
- Reference condition
- NIST reference EMF is relative to 0°C unless compensation is applied.
Worked Type K Thermocouple Examples
100°C with a 0°C reference
Assumption: nominal homogeneous Type K materials and an ideal 0°C reference. NIST gives EK(100°C) ≈ 4.096 mV and EK(0°C) = 0 mV.
Result: 4.096 − 0.000 = 4.096 mV. A real reading may differ because this is a reference function, not an accuracy specification.
100°C with a 25°C reference
Assumption: the terminal/reference junction is actually 25°C. Its nominal Type K equivalent is about 1.000 mV.
Result: 4.096 − 1.000 ≈ 3.096 mV measured. Treating 3.096 mV as a 0°C-reference signal would understate the hot-junction temperature.
Reverse a compensated measurement
Given: 3.096 mV measured and a 25°C reference. Add about 1.000 mV to obtain about 4.096 mV equivalent at a 0°C reference.
Result: the bounded inverse function returns approximately 100°C. Confirm that the compensated EMF is within −5.891 to 54.886 mV before converting.
Reference Function Is Not Measurement Accuracy
The calculator describes the nominal Type K temperature–EMF relationship. A complete uncertainty assessment also considers the sensor, instrument, junctions, wiring, environment, and calibration history.
| Error source | Possible effect | Practical check |
|---|---|---|
| Thermocouple tolerance | Probe EMF differs from the ideal reference function. | Use the governing wire/probe specification or calibration certificate. |
| Reference-junction error | Direct temperature bias after compensation. | Verify terminal temperature sensing and isothermal construction. |
| Wrong extension wire or connector | Unwanted junction EMFs. | Confirm Type K-compatible materials throughout the circuit. |
| Drift and inhomogeneity | Reading changes with thermal history or gradient location. | Inspect exposure history and recalibrate or replace when justified. |
| Noise and instrument error | Unstable or biased millivolt measurement. | Check shielding, grounding, input specification, and a known source. |
Common Type K mistakes
- Assuming every terminal block is a 0°C reference junction.
- Reversing polarity or mixing Type K with another thermocouple type.
- Substituting ordinary copper wire where Type K-compatible extension materials and compensation are required.
- Confusing millivolts with microvolts—a factor of 1000.
- Extrapolating beyond a published polynomial range.
- Treating the reference-function limits as the operating rating of every probe.
Source, Scope, and Data-Rights Notes
Calculated nominal Type K ITS-90 checkpoints and conversion; source checked August 9, 2026.
The converter evaluates published NIST Type K reference and inverse functions. The limited table is calculated and rounded by Turn2Engineering; it is not an official NIST table or a substitute for a governing equipment specification.
- NIST Temperature Scale Database, Standard Reference Database 60Type K reference convention, functions, ranges, and official table access.
- NIST Monograph 175: Temperature-Electromotive Force Reference Functions and TablesType K direct function, positive-range exponential correction, bounded inverse functions, and ITS-90 basis.
- ASTM E230/E230M-23aPublic scope confirms standardized thermocouple reference data and the distinction between reference relationships and tolerances; proprietary tables are not reproduced.
- BIPM Guide to Secondary Thermometry—Thermocouple Thermometry, Part 1Measurement principles, reference junctions, inhomogeneity, installation, and uncertainty context.
Dataset and Source-Check Details
- Publisher
- Turn2Engineering
- Dataset label
- Calculated from NIST Monograph 175 Type K ITS-90 functions; checked against NIST SRD 60 Version 3.0, data content 2024
- Coefficient check
- Type K coefficient transcription and regression checkpoints verified August 9, 2026
- Canonical units
- Degrees Celsius and millivolts relative to 0°C
- Valid ranges
- Forward −270°C to 1372°C; inverse approximately −200°C to 1372°C
- Calculated fields
- °F, µV, differential EMF, compensated EMF, and local sensitivity
- Excluded
- Probe tolerances, equipment ratings, calibration claims, color codes, and other thermocouple types
- Rights decision
- No complete SRD or ASTM table and no full-dataset CSV; only a limited calculated subset is displayed
- Reference condition
- Nominal Type K materials on ITS-90; 0°C reference unless compensation is entered
K Type Thermocouple Chart FAQs
Approximately 4.096 mV nominal with a 0°C reference junction. A nonzero reference-junction temperature changes the differential voltage actually measured.
First adjust the measured voltage for the reference-junction temperature. Then apply the correct bounded inverse function to the equivalent 0°C-reference EMF.
The chart is an ideal reference function. Wire tolerance, cold-junction error, instrument accuracy, connections, gradients, drift, noise, and installation can all change the observed reading.
No. That is the nominal reference-function range. Actual limits depend on probe construction, sheath, wire size, insulation, atmosphere, manufacturer, and the governing specification.
No. The relationship is monotonic across the reference range but nonlinear, so one constant µV/°C approximation should not replace the reference function.
Use the Converter for the Actual Reference Junction
The table is a fast nominal lookup for a 0°C reference. For field or instrument signals, enter the real reference-junction temperature, keep the calculation within the published range, and apply the sensor and instrument uncertainty required by the job.