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Type K Thermocouple – Complete Guide for Industrial Use (US)
Everything you need to know about Type K thermocouples: construction, accuracy, output, color codes, and common U.S. applications.
What Is a Type K Thermocouple?
Type K thermocouples are the most common industrial thermocouple, made from Nickel-Chromium (Chromel) and Nickel-Aluminum (Alumel). They offer reliable, cost-effective temperature measurement across a wide range, especially in oxidizing and inert environments.
Type K Thermocouple Composition
- Positive leg (Chromel): ~90% Nickel, 10% Chromium
- Negative leg (Alumel): ~95% Nickel with small amounts of Aluminum, Manganese, and Silicon
Type K Thermocouple Accuracy & Tolerances
Type K thermocouples, made from Nickel-Chromium (+) and Nickel-Aluminium (–) conductors, are widely used due to their accuracy and broad temperature range. They typically generate around 39–43 µV/°C depending on the measured temperature.
According to ASTM E230 standards, tolerances are:
- Standard: ±2.2°C or ±0.75% of reading
- Special Limits: ±1.1°C or ±0.4% of reading
Under IEC 60584-1 tolerances:
- Class 1: ±1.5°C up to 375°C, then ±0.004 × |t|
- Class 2: ±2.5°C up to 333°C, then ±0.0075 × |t|
- Class 3: For –200°C to +40°C, up to ±0.015 × |t|
Typical working range is 0°C to 1260°C (32°F to 2300°F). For critical low-temperature applications, material selection may be required to meet Class 3 limits.
Type K - Technical Data
| Conductor Combination | Approximate EMF Change (µV/°C) Referenced to 0°C at: |
Approximate Working Temperature Range | Initial Calibration Tolerances (ASTM E-230) | Thermocouple Output Tolerances (IEC 60584-1) | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| + Leg | - Leg | 100°C | 500°C | 1000°C | °F | °C | Standard | Special | Type | Class 1 | Class 2 | Class 3 |
| Nickel-Chromium Also known as: Chromel™, Thermokanthal KP*, NiCr, T1*, Tophel™ |
Nickel-Aluminium (magnetic) Also known as: Alumel™, Ni-Al, Thermokanthal KN™, T2™, NiAl™ |
42 | 43 | 39 | 32 to 2300 | 0 to 1260 | ±2.2°C or ±0.75% | ±1.1°C or ±0.4% |
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| |
–167°C to +40°C ±2.5°C –200°C to –167°C ±0.015 × |t| |
1. Tolerance is expressed either as a fixed deviation in °C or as a percentage of the actual temperature.
2. Thermocouple materials are typically supplied to meet tolerances for temperatures above –40°C. For Class 3 accuracy below this range, materials must be specially selected — this should be stated when ordering.
Color Code (ANSI Standard – US)
Type K thermocouples in the U.S. follow ANSI color coding:
- Positive (+): Yellow
- Negative (−): Red
- Overall Jacket: Yellow (for extension grade)
In the United States, thermocouple wire color codes and tolerances are standardized under ANSI MC96.1 (1982) and ASTM E230. Per these standards, extension and compensating extension wire is identified by adding an “X” to the thermocouple type (e.g., KX). Thermocouple-grade wire typically features a brown overall jacket, while extension wire uses an overall jacket matching the color of the positive leg. In some insulations, colors may appear as a stripe or tracer. Note that high-temperature braided insulation is usually not color coded.
The table below shows the color coding adopted by the ASTM and IEC. Please click here for all thermocouple wire color codes including type T (copper vs constantan), Type J (iron vs constantan) etc.
| ANSI MC96.1 United States | International
Color Code to IEC 60584-3 |
Redundant national colors | ||
|---|---|---|---|---|
| Thermocouple Grade | Extension Grade | BS 1843 | DIN 43714 |  |  |  |  |  |
Explore our in-depth Thermocouple & RTD Guide — a technical resource developed for engineers and specifiers. Covers sensor selection, installation practices, standards and tolerances, colour codes, wiring configurations, sensor theory and more.
Applications of Type K Thermocouples
Type K thermocouples are ideal for a range of industrial and scientific applications, including:
- Industrial process control
- Heat treatment furnaces
- HVAC systems
- Engine exhaust measurements
- Scientific labs
Type K Thermocouple Sensors for Common Temperature Measurement Applications
Type K Mineral Insulated
Thermocouples
Rugged sensors, ideal for most applications. Vast choice of terminations e.g. pot seals, cables, connectors, heads etc. Usually ungrounded.
Swaged TipThermocouples
Fast response thermocouples with a smaller probe tip, ideal for industrial and other applications.
Type K Miniature
Thermocouples
Ideal for precision temperature measuring where minimal displacement and a fast response is required.
K Type Heavy Duty
Thermocouples
For industrial temperature measurement applications such as furnaces, kilns, ovens, boilers, flues etc. Many types of sheath material available.
General Purpose
Type K Thermocouples
A wide range of K type thermocouples to suit many applications. Simple bead style thermocouples, Hand held, surface, bayonet, bolt, patch styles etc.
ATEX/IECEx ApprovedThermocouples
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A large range of thermocouples with a variety of terminations such as pot seal, terminal heads etc.
Ordering Type K Thermocouples (US Supply)
We manufacture Type K thermocouples to custom specifications with a range of sheath materials, insulation types, and terminations. Shipping across the USA with fast turnaround times.
Quick FAQs About Type K Thermocouples
- What is the temperature range of a Type K thermocouple?
Typically 0°C to 1260°C (32°F to 2300°F), depending on insulation and design. - Is Type K thermocouple magnetic?
The negative leg (Alumel) is magnetic; the positive leg (Chromel) is not. - What is the voltage output of a Type K thermocouple?
Approximately 39–43 µV/°C depending on the temperature. - What color is a Type K thermocouple?
In the U.S., the positive leg is yellow, the negative is red, and the overall jacket is yellow (ANSI standard).