A measuring apparatus (1), for the contactless determination of a temperature (T) of an object (100), e.g., of a human, has an infrared camera (10) with a focus (11). A calibrating device (30) is connected to the infrared camera (10) via a data link. The calibrating device (30) has an outer shell (31) with an emissivity on the outside similar to that of the object (100). A temperature sensor (34) is arranged in the outer shell (31). Moreover, a method for contactless determination of a temperature (T) of an object (100) with the measuring apparatus (1) as well as a method for the operation of the measuring apparatus are provided.