The principle behind thermocouple wire is that the joining of two alloys exposed to certain temperature will create a specific voltage. A different temperature will produce a different voltage. Essentually temperature can be measured using thermocouple wire and equipment that can translate the voltage reading into a corresponding temperature. Those two alloys are the wire's Calibration.

Calibrations fall into three categories.

• Themocouple Special Limits of Error
• Thermocouple Wire
• Thermocouple Extension

Calibration Type	Temperature Range		Tolerances (whichever is greater)
	°F	°C	Standard	Special
Thermocouple-Grade Wire
J	32 to 1382°F	0 to 750°C	±2.2°C or ±0.75%	±1.1°C or ±0.4%
K	32 to 2282°F	0 to 1250°C	±2.2°C or ±0.75%	±1.1°C or ±0.4%
E	32 to 1652°F	0 to 900°C	±1.7°C or ±0.5%	±1.0°C or ±0.4%
T	32 to 662°F	0 to 350°C	±1.0°C or ±0.75%	±0.5°C or ±0.4%
R or S	32 to 2642°F	0 to 1450°C	±1.5°C or ±0.25%	±0.6°C or ±0.1%
B	1598 to 3092°F	870 to 1700°C	±0.5°C
N	32 to 2282°F	0 to 1250°C	±2.2°C or ±0.75%	±1.1°C or ±0.4%
Extension-Grade Wire
JX	32 to 392°F	0 to 200°C	±2.2°C	±1.1°C
KX	32 to 392°F	0 to 200°C	±2.2°C	±1.1°C
EX	32 to 392°F	0 to 200°C	±1.7°C	±1.0°C
TX	32 to 212°F	0 to 100°C	±1.0°C	±0.5°C
NX	32 to 392°F	0 to 200°C	±2.2°C	±1.1°C
Compensating Extension Wire
BX	32 to 392°F	0 to 200°C	±3.7°C
CX	32 to 1600°F	0 to 870°C	±6.8°C
RX or SX	32 to 392°F	0 to 200°C	±5.0°C