This paper investigates user–level (or perceptual) QoS of audio–video transmission over IP networks with terminals of different size monitors. As the first step of our research, we treat large-sized monitors. By experiment, we assess the user–level QoS for three monitor sizes (80, 60 and 40 inches) and perform QoS mapping. In our experiment, we changed the monitor size by using a projector. The user–level QoS is assessed by the method of successive categories, which is one of the psychometric methods. Moreover, we performed QoS mapping from application–level to user–level with multiple regression analysis. The experimental result indicates that when the degradation of the quality of the audio–video transmission is not noticeable, the user–level QoS of the large monitor size (i.e., 80 inch) becomes the highest. We also observe that when we can notice a low level of degradation of the transmission, the user–level QoS parameter of the large monitor size becomes the smallest. When the degradation is too much, we hardly notice any difference in the user–level QoS between the monitor sizes. We thus confirmed that the monitor size is one of important application–level QoS parameters we must consider.