Before you start working on your poster presentation you have to decide what size to make your poster. Each conference publishes poster session guidelines indicating the space they are making available for poster presentations. You would need to follow their instructions or you may end up with a poster that is too big or too small for the available space. It is common for conferences in the United States to provide a 4x8 foot space (48x96 inches) to the attendees, but not always, so be careful. Conferences outside the US most often provide smaller spaces and ask for vertical or square scientific posters (tall and narrow) in metric measurements.
If the conference is providing a 4x8 space, here is a visual example of how some commonly used size posters will fit in that space.
As you can see in the above diagram, you have many poster size options. To determine which size is best for your poster presentation you should look at the amount of information you want to present. Will your poster be mostly text, or a combination of text, graphs, charts, tables and photos? Most likely, your presentation is going to be a mix of all of the above. Look at your source document(s). How many pages of text do you have? Assuming that you want to include pictures, tables, etc. in your poster, the table below will give you a general idea of what size poster you may be able to make without having to make the text too small or too big. Please remember that this is a VERY general guide.