What settings do I use in PowerPoint if I want to create a graphic other than 400 pixels wide by 400 pixels high?
Divide the desired dimension in pixels by 96 to determine the setting for PowerPoint’s Page Setup dialog box. For example, if you want to create a graphic that is 400 pixels wide by 200 pixels high, set the PowerPoint width to 4.17 inches and the height to 2.08 or 2.09. The reason for this is that PowerPoint outputs its slides at 96 pixels per inch resolution when you save the slides in GIF or JPEG format.
