Thermocouple vacuum gauge consists of glass bottle whose one end is connected to gas whose pressure is to determined. Inside the bottle there is resisting heating element made up of tungsten wire which is connected to external supply. and to this element thermocouple is welded. here thermocouple is connected to pmmc which is directly reads value of pressure. temperature of heater depends upon two parameters i.e. amount of current and thermal conductivity of surrounding gas. at constant current and temperature of heater depends only on thermal conductivity of surrounding gas. pressure of gas increases, the thermal conductivity also increases. EMF of thermocouple which is noted on pmmc and directly calibrated to amount of pressure. in this way we can determine the value of low pressure. this gauge is used to measure the vacuum pressure. in low pressure zone, pressure of gas is directly proportional to thermal conductivity of gas.