A video decoder can be configured to decode a first syntax element indicating a size of a coding tree unit (CTU); after decoding the first syntax element indicating the size of the CTU, decode a second syntax element indicating a width of elements of a subpicture identifier grid; after decoding the first syntax element indicating the size of the CTU, decode a third syntax element indicating a height of the elements of the subpicture identifier grid; and determine a location of a subpicture within a picture based on the first syntax element, the second syntax element, and the third syntax element.