The sensitivity of modern thermocouple is around o.1C over a range which spans from -270C to 1750C. Here is an app note from Maxim on how to built high precision temperature acquisition systems based on thermocouple sensors.
One examples uses a 24bit ADCs for high precision measurement. Another example use a MAX31855 thermocouple-to-SPI converter for designs that don’t require high precision.
Thermocouples are used in a wide range of temperature-sensing applications. Recent developments in thermocouple designs, as well new standards and algorisms, have greatly extended their temperature ranges and precision. Accuracies up to ±0.1°C are now possible over a very wide -270°C to +1750°C range. To utilize all the new thermocouple capabilities, high-resolution thermocouple temperature-measurement systems are required. A low-noise, 24-bit, delta-sigma analog-to-digital converter (ADC) with the ability to resolve very small voltages perfectly fits this task.