Depends if your looking from the perspective of a VTT or a print product. If your intension is to print the squares need to be 1 inch to accommodate mini's for gameplay. If it's a VTT you general go either 50-100 px per square to accommodate lower file size for hosting and keep efficiency of usage. If you are doing it just to show a representation of the dungeon so then can replicate it on a dry erase etc.