# K — Thermocouple type letter to alloy pair, ANSI/IEC color code and tolerance class

For K, positive-leg alloy is Chromel; negative-leg alloy is Alumel; ansi/astm positive-leg color is Yellow; ansi/astm negative-leg color is Red; ansi extension-grade jacket color is Yellow, verified against its source on 2026-08-19.

- **Type letter:** K _(verified: appears in the quote below)_
- **Positive-leg alloy:** Chromel _(verified: appears in the quote below)_
- **Negative-leg alloy:** Alumel _(verified: appears in the quote below)_
- **ANSI/ASTM positive-leg color:** Yellow _(verified: appears in the quote below)_
- **ANSI/ASTM negative-leg color:** Red _(verified: appears in the quote below)_
- **ANSI extension-grade jacket color:** Yellow _(verified: appears in the quote below)_
- **Source document:** ANSI/ASTM Thermocouple Color Codes _(verified: appears in the quote below)_
- **Usable temperature range:** –270 to 1372°C _(per assets.omega.com, not stated by the source above)_
- **IEC 60584 Class 1 tolerance:** –40°C to +375°C ±1.5°C 375°C to 1000°C ±0.004 ⋅ |t| _(per tc-inc.com, not stated by the source above)_
- **IEC 60584 Class 2 tolerance:** –40°C to +333°C ±2.5°C 333°C to 1200°C ±0.0075 ⋅ |t| _(per tc-inc.com, not stated by the source above)_
- **IEC 60584-3 positive-leg color:** Green _(per tc.co.uk, not stated by the source above)_
- **IEC 60584-3 negative-leg color:** White _(per tc.co.uk, not stated by the source above)_
- **IEC 60584-3 outer sheath colour:** Green _(per tc.co.uk, not stated by the source above)_

## What the source says

> Type | Positive conductor | Negative conductor | Positive color | Negative color | Extension-grade jacket | Thermocouple-grade jacket shown in legacy assets | T | Copper | Constantan | Blue | Red | Blue | Brown | J | Iron | Constantan | White | Red | Black | Brown | E | Chromel | Constantan | Purple | Red | Purple | Brown | K | Chromel | Alumel | Yellow | Red | Yellow | Brown |

## Sources disagree

More than one authority states this, and they do not state the same
thing. Both are reproduced with the source each came from.

### Source document

thermometricscorp.com says source document is **ANSI/ASTM Thermocouple Color Codes**, as of 2026-08-19.

> Type | Positive conductor | Negative conductor | Positive color | Negative color | Extension-grade jacket | Thermocouple-grade jacket shown in legacy assets | T | Copper | Constantan | Blue | Red | Blue | Brown | J | Iron | Constantan | White | Red | Black | Brown | E | Chromel | Constantan | Purple | Red | Purple | Brown | K | Chromel | Alumel | Yellow | Red | Yellow | Brown |

Source: https://thermometricscorp.com/thermocouple-color-codes.html

assets.omega.com says source document is **ANSI and IEC Color Codes**, as of 2026-08-19.

> ALOMEGA ® Clean Oxidizing and Inert. + + CHROMEGA ® + + K K Limited Use in Vacuum NICKEL- NICKEL- – – ALUMINUM or Reducing. Wide –270 to 1372°C –6.458 to – – CHROMIUM Temperature Ni-AI Range, Most Popular –454 to 2501°F 54.886 Ni-Cr (magnetic) H Calibration

Source: https://assets.omega.com/pdf/test-and-measurement-equipment/temperature/sensors/thermocouple-probes/tc_colorcodes.pdf

tc-inc.com says source document is **Thermocouple Tolerances**, as of 2026-08-19.

> Thermocouple Output Tolerances to IEC 60584-1 | Type | + Leg | - Leg | 100ºC | 500ºC | 1000ºC | Continuous | Short Term | Type | Class 1 | Class 2 | K | NICKEL - CHROMIUM Also known as: Chromel™, Thermokanthal KP*, NiCr, T1*, Tophel™ | NICKEL - Aluminum (magnetic) Also known as: Ni-Al, Alumel™, Thermokanthal KN™, T2™, NiAl™ | 42 | 43 | 39 | 0 to +1100ºC | -180 to +1350ºC | Temperature Range Tolerance Value Temperature Range Tolerance Value | –40°C to +375°C ±1.5°C 375°C to 1000°C ±0.004 ⋅ |t| | –40°C to +333°C ±2.5°C 333°C to 1200°C ±0.0075 ⋅ |t|

Source: https://www.tc-inc.com/thermocouple/thermocouple-tolerances.html

tc.co.uk says source document is **Thermocouple Colour Code Standards**, as of 2026-08-19.

> What is the Colour Code for a Type K Thermocouple? In the UK and Europe, the most widely used colour code for Type K thermocouple cable is to the international IEC 60584-3 standard which is as follows: Positive Leg = Green, Negative Leg = White, Outer Sheath (Jacket) = Green, Thermocouple Connector Colour = Green

Source: https://www.tc.co.uk/thermocouple-information/thermocouple-colour-code.html


## Source

- https://thermometricscorp.com/thermocouple-color-codes.html
- https://assets.omega.com/pdf/test-and-measurement-equipment/temperature/sensors/thermocouple-probes/tc_colorcodes.pdf
- https://www.tc-inc.com/thermocouple/thermocouple-tolerances.html
- https://www.tc.co.uk/thermocouple-information/thermocouple-colour-code.html

Last verified: 2026-08-19. Review by: 2028-08-18.
Part of [Thermocouple type letter to alloy pair, ANSI/IEC color code and tolerance class](https://referencesource.org/thermocouple-type-color-code-crosswalk/).