Temperature Measurement Cheat Sheet
RTD and thermocouple essentials on one page: conversions, Pt100 resistance values and classes, the Callendar–Van Dusen equation, thermocouple types, millivolts and colour codes.
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A one page A4 sheet to print, pin up in the workshop or keep on your phone. Everything on it is also shown below.
Download PDF A4 · 87 KBTemperature units
| Fahrenheit | °F = °C × 9 ÷ 5 + 32 |
| Kelvin | K = °C + 273.15 |
| Rankine | °R = °F + 459.67 |
| Interval | 1 °C (or 1 K) = 1.8 °F |
Pt100 resistance (IEC 60751)
| °C | Ω | °C | Ω |
|---|---|---|---|
| −50 | 80.31 | 200 | 175.86 |
| 0 | 100.00 | 300 | 212.05 |
| 50 | 119.40 | 400 | 247.09 |
| 100 | 138.51 | 500 | 280.98 |
| 150 | 157.33 | 600 | 313.71 |
Pt1000: multiply by 10. α = 0.00385 Ω/Ω/°C, about 0.385 Ω per °C for Pt100.
Callendar–Van Dusen
| 0 °C and above | R = R0 (1 + A t + B t²) |
| Below 0 °C | R = R0 [1 + A t + B t² + C (t − 100) t³] |
| Constants | A = 3.9083 × 10⁻³, B = −5.775 × 10⁻⁷, C = −4.183 × 10⁻¹² |
RTD tolerance classes (IEC 60751)
| Class | Tolerance (°C) |
|---|---|
| AA | ± (0.10 + 0.0017 |t|) |
| A | ± (0.15 + 0.002 |t|) |
| B | ± (0.30 + 0.005 |t|) |
| C | ± (0.60 + 0.01 |t|) |
Thermocouple types
| Type | Materials | Typical range °C | mV at 100 °C |
|---|---|---|---|
| K | NiCr / NiAl | −200 to 1200 | 4.096 |
| J | Fe / CuNi | −40 to 750 | 5.269 |
| T | Cu / CuNi | −200 to 350 | 4.279 |
| E | NiCr / CuNi | −200 to 900 | 6.319 |
| N | NiCrSi / NiSi | −200 to 1200 | 2.774 |
| R | Pt13Rh / Pt | 0 to 1600 | 0.647 |
| S | Pt10Rh / Pt | 0 to 1600 | 0.646 |
| B | Pt30Rh / Pt6Rh | 600 to 1700 | 0.033 |
mV values from the IEC 60584-1 / NIST reference tables, cold junction at 0 °C.
Thermocouple colours (positive / negative)
| Type | IEC 60584-3 | ANSI MC96.1 |
|---|---|---|
| K | Green / white | Yellow / red |
| J | Black / white | White / red |
| T | Brown / white | Blue / red |
| E | Violet / white | Purple / red |
| N | Pink / white | Orange / red |
| R, S | Orange / white | Black / red |
| B | Grey / white | Grey / red |
ANSI: the negative wire is always red.
RTD vs thermocouple
- RTD: more accurate and stable, up to about 600 °C
- Thermocouple: wider range (to 1700 °C), faster, rugged, needs cold junction compensation
- Use 3 wire RTD to cancel lead resistance; 4 wire for laboratory accuracy
- Use extension or compensating cable of the same type for thermocouples
Cold junction
| Measured | Emeas = E(Thot) − E(Tcj) |
| So | E(Thot) = Emeas + E(Tcj), then convert to °C |
Related Calculators and Tools
Frequently Asked Questions
What is the resistance of a Pt100 at 0 °C?
100.00 Ω. At 100 °C it is 138.51 Ω.
Which thermocouple is most common?
Type K, for its wide range (about −200 to 1200 °C) and low cost.
Why is the red wire negative on US thermocouples?
ANSI MC96.1 makes the negative conductor red for every type, so the polarity is always easy to identify.
Learn more on the blog
Common types of thermocouples and their ranges
A practical guide on instrumentationblog.in that explains the theory behind this cheat sheet.
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