According to the search results, a 1/2 inch x 1/2 inch square notch trowel is a good trowel size for 12x24 wall tiles. This size is also recommended for most tiles that are 16 inches and larger, including 24x24 tiles, 16x16 tiles, 6x24 tiles, 8x36 tiles, and wood-look plank tiles. It is also a good choice for natural stone tiles 12x12 and larger like marble, granite, and travertine. It is important to note that the size of the trowel depends on the size and type of tile being installed, as well as the flatness of the substrate.