Methods, devices and systems for signaling the use of subpictures in coded video pictures are described. One example method of video processing includes performing a conversion between a video and a bitstream of a video, wherein the bitstream conforms to a format rule, and wherein the format rule specifies that a first syntax element, which indicates whether a picture of the video can be partitioned, is conditionally included in a picture parameter set (PPS) of the bitstream based on values of a second syntax element, which indicates whether identifiers of subpictures are signaled in the PPS, and a third syntax element, which indicates, in the PPS, a number of the subpictures.