If you print many documents, you might have wondered how many odd formats your printer driver can handle. Not surprisingly, paper sheets come in many more sizes than just the standard letter and A4 paper.
If you must format the printout, check the paper format. You can get this information from the Windows API or directly from the printer object or class in your development language.
Do not expect only one of these sizes because user-defined types might be used. For example, professional output devices might have sizes like A4+ for borderless A4 output.