 Open a PowerPoint and choose New, Blank Presentation. Then select the Design tab on top and find Slide Size. Choose Custom Slide Size and make your width 30 inches and your height 40 inches, making sure Portrait is selected as well. Click OK and PowerPoint will ask you if you want to maximize or ensure fit. We recommend choosing Ensure Fit so that you can see the whole thing at once. Then on your Home tab, select the Layout drop-down menu and choose Blank. Now go ahead and do a Save As using the File tab and name your poster project and choose a place to save it too.