A method and an apparatus for determining an RBG size are provided. In the method, a network device or a terminal determines an RBG size set, where the RBG size set may include one or more possible RBG sizes; and determines a first RBG size included in the RBG size set. The network device allocates a resource to the terminal by using the determined first RBG size. The terminal determines, based on the determined first RBG size, the resource allocated by the network device to the terminal.