EMF Output vs Temperature
A thermocouple produces a small voltage (electromotive force, EMF) that varies with the difference in temperature between its measuring junction and its reference (cold) junction. The reference tables in this section give the millivolt output of each thermocouple type as a function of measuring junction temperature, with the reference junction held at exactly 0 °C.
All values are tabulated on the International Temperature Scale of 1990 (ITS-90) and are identical to the NIST polynomial coefficients reproduced in NIST Monograph 175 (1993). The same values appear in ASTM E230 and in the harmonized IEC 60584-1:2013 standard — to within rounding at the last digit shown.
Why a 0 °C Reference?
Historically, the cold junction was placed in an ice bath. Modern instruments use electronic cold-junction compensation: a separate temperature sensor measures the actual reference-junction temperature, looks up the equivalent EMF on the same table, and adds it to the raw EMF reading before converting back to temperature. The cold-junction correction is the single largest source of error in most thermocouple measurements.
- EMF is non-linear — never use a single µV/°C value across a wide range
- Always re-zero to the actual cold junction temperature
- Use matching extension wire from cold junction back to the measuring instrument
- Polarity matters — the (+) lead is the alphabetically first material in the pair
Sign Convention
EMF is positive when the measuring junction is hotter than the reference junction. EMF values below 0 °C are negative — for example, Type K at -100 °C is -3.554 mV.
ITS-90 Polynomials
For software implementations, use the NIST inverse polynomials (mV → °C) rather than table interpolation. Polynomials are piecewise — typically three or four sub-ranges per type. Full coefficients are tabulated in NIST Monograph 175 and are referenced in our calibration software.
Standards in Force
NIST Monograph 175 (1993)
ASTM E230 / E230M-17
IEC 60584-1:2013
IEC 60584-3:2007 (color codes)
ANSI MC96.1 (US color codes)
All 8 Standardized Thermocouple Types
Temperature range is the standard published range — practical operating temperature is usually 50 °C below the upper limit for continuous service to preserve calibration. Noble metal types (R, S, B) are platinum-based and an order of magnitude more expensive than base metal types.
| Type | Temperature Range | Conductor Materials (+/–) | Sensitivity | Typical Applications |
|---|---|---|---|---|
| Type B | 0 to +1820 °C | Pt-30%Rh (+) / Pt-6%Rh (–) | ~10 µV/°C @ 1500 °C | Glass furnaces, sapphire growth, high-temp metallurgy, kilns |
| Type E | -270 to +1000 °C | Ni-Cr (+) / Cu-Ni (–) (Chromel/Constantan) | ~76 µV/°C @ 500 °C — highest of all base metal types | Cryogenic, sub-zero, low-temperature accurate measurement |
| Type J | -210 to +1200 °C | Iron (+) / Cu-Ni (–) (Iron/Constantan) | ~55 µV/°C @ 0 °C | Older plants, vacuum processes, reducing atmospheres |
| Type K | -270 to +1372 °C | Ni-Cr (+) / Ni-Al (–) (Chromel/Alumel) | ~41 µV/°C @ 0 °C | General-purpose industrial — the most common thermocouple |
| Type N | -270 to +1300 °C | Nicrosil (Ni-Cr-Si) / Nisil (Ni-Si) | ~39 µV/°C @ 0 °C | Replacement for Type K — better stability above 1000 °C |
| Type R | -50 to +1768 °C | Pt-13%Rh (+) / Platinum (–) | ~12 µV/°C @ 1000 °C | Heat treating, calibration, sulfur-free oxidizing atmospheres |
| Type S | -50 to +1768 °C | Pt-10%Rh (+) / Platinum (–) | ~10 µV/°C @ 1000 °C | Defined ITS-90 reference — calibration, precious metal refining |
| Type T | -270 to +400 °C | Copper (+) / Cu-Ni (–) (Copper/Constantan) | ~43 µV/°C @ 0 °C | Food, pharma, cryogenic, mild-temperature general use |
Detailed Reference by Type
Type K — Chromel/Alumel
The general-purpose industrial thermocouple. Range -270 to +1372 °C, sensitivity ~41 µV/°C at 0 °C, oxidizing or inert atmospheres. Full chart with 50 °C increments and tolerance bands.
View full Type K chartType J — Iron/Constantan
Range -210 to +1200 °C. Iron leg oxidizes rapidly above 540 °C; best for reducing or vacuum atmospheres. Sensitivity ~55 µV/°C, slightly higher than Type K but limited maximum temperature and a "magnetic transition" anomaly at 770 °C.
Detailed chart on requestType T — Copper/Constantan
Range -270 to +400 °C. Excellent accuracy and stability below 0 °C — Class 1 tolerance bands are tighter than any other base-metal type at cryogenic temperatures. Copper conductor susceptible to corrosion above 370 °C in oxidizing atmospheres.
Detailed chart on requestType E — Chromel/Constantan
Range -270 to +1000 °C. Highest sensitivity of any standard thermocouple (~76 µV/°C at 500 °C) — preferred when signal-to-noise ratio is critical, particularly in low-temperature work and cryogenic instrumentation.
Detailed chart on requestType N — Nicrosil/Nisil
Range -270 to +1300 °C. Designed as a successor to Type K — substantially better long-term stability above 1000 °C, with minimal "green rot" degradation in low-oxygen atmospheres. Slightly lower sensitivity than Type K (~39 vs 41 µV/°C).
Detailed chart on requestType R — Pt-13%Rh / Pt
Noble metal type. Range -50 to +1768 °C with excellent long-term stability above 1000 °C. Used in heat treating, semiconductor processing, sapphire growth, and as a transfer-standard reference thermocouple in calibration laboratories.
Detailed chart on requestType S — Pt-10%Rh / Pt
Range -50 to +1768 °C. Historically the defining thermocouple for ITS-68 between 630.74 and 1064.43 °C — still used as a primary reference in metallurgical and precious-metal industries. Very similar to Type R but with a flatter sensitivity curve.
Detailed chart on requestType B — Pt-30%Rh / Pt-6%Rh
Highest temperature standardized thermocouple. Range 0 to +1820 °C — used in glass manufacturing, kilns, and ultra-high-temperature furnaces. Output is essentially zero below 50 °C, so cold-junction compensation is uncritical, but signal is small (~10 µV/°C at 1500 °C).
Detailed chart on requestITS-90, ASTM E230 & IEC 60584
The three reference documents below provide essentially the same EMF-temperature relationships. Any discrepancies are at the last-rounded-digit level. Choose the standard your industry calls out.
NIST Monograph 175
The U.S. primary reference. Contains the full polynomial coefficients for every standardized thermocouple type on ITS-90, with cold-junction reference at 0 °C. Published 1993, still authoritative. Free PDF download from NIST.
ASTM E230 / E230M
The U.S. consensus standard. Republishes the NIST tables in tabular and graphical form and adds three tolerance classes — Standard, Special, and Sub-Special — together with letter-code color identifications under ANSI MC96.1.
IEC 60584
The international standard (three parts). Part 1 — EMF tables. Part 2 — tolerance Classes 1, 2, and 3. Part 3 — extension wire and compensating cable color codes. Harmonized with NIST values; widely adopted in Europe and Asia.
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