There are a variety of paper sizes available that you can use for various printing needs.
This picture below would give you an understanding of papers and help you make better decisions when you want to print.
A1: This can be used to print materials like Calendars, Posters, Carrier bags and others.
A2: This size is suitable for printing on Calendars, Brochures, Posters and Carrier bags.
A3: Calendars, Brochures, Programs and Magazines.
A4: Flyers, Letterheads, Invitation Cards, Notebooks and Invoices.
A5: Flyers, Greeting Cards, Table Calendars, Invoice and Note pads.
P. S: These paper sizes are not limited to this materials only.