Remember Marketing's slide? It had text so small it became too hard to read here in a printed book. Imagine trying to read the slide when it is projected fifteen feet away!
Just because there is more content than will fit on a slide, do not make the fonts so small the participants can't see them. If there is too much content to allow an adequate font size, then split the slide into two slides!
The right size is large enough so all participants can read the text from a reasonable distance. Because the distance depends on the type of presentation being created, let's look at the two basic types of presentations separately.
Text on a speaker-led presentation should never be smaller than 24 point. In addition, most text on speaker-led presentations should be at least 36 points, which allows the font to be visible from a reasonable distance when projected.
Text in PowerPoint title placeholders should be 54 to 72 points in size. This is not always possible because it makes the number of characters per line too short, so the smallest title text should be is 12 points larger than the other text on the slide.
If text is to be animated, test the font and size combinations on a projection screen before making any final size decisions.
A general rule of thumb for speaker-led presentations is to have no more than ten lines of text on any slide, including the slide's title. Besides ensuring the text is large enough to be visible to all participants, this rule ensures content on any given slide is cohesive and connected.
Because animated and kiosk presentations are generally developed for one viewer at a time, the font sizes can be smaller. General text can be as small as 14 point, title text can be as small as 26.
Just because a smaller font is being used does not mean an overload of information ought to be presented on a single slide. Be sure someone views sample slides for readability before finalizing the presentation design.
Because different fonts interpret the point sizes differently, be sure sample slides are created and tested before font choices are finalized. Remember the best test for font choices is really participant comprehension . If the text is hard for participants to read and interpret, then they are too small.