I am not replying as an expert. Without Photo Shop at 240 dots/inch (dpi) about 18x12inches or 45x30cm If you add some pixels with Photo Shop (and I presume with other PP-programs), with ease double the size that is 36x24 inches. If you are prepared to less dense dpi the pictures can be bigger but you will need to look at distance to prevent seeing the individual pixels. If you are really fussy and are need of very high quality pictures and the printer can handle it, use 300 dpi (the international standard). In the real world, as big a picture size as you will ever want.