The size of text on PowerPoint slides matters! If it is not clearly readable by everyone it adds frustration and creates a distraction. I’ve heard too many presenters say “You may not be able to read this, but …” If that is the case, then why even show the slide?
There is an old rule of thumb in the presentation world called the 8H Rule of Legibility. The rule was developed as a guideline when 35 mm slides were in use. The rule goes like this: If you can read an image from a distance of eight times its height, odds are that everyone will be able to read it when projected.
In those days, if you could read a 35 mm slide, which was 1 inch in height, from 8 inches away, that slide would be legible under most presentation conditions.
Translated in today’s world, if your computer screen is 10 inches in height, scoot away from your screen 80 inches. If you can read it, then you are probably okay. In practical terms, that means that you should never go below 11 points. I think 18 points is a safer number, but obviously, 22 or 24 points gives you extra wiggle room in the event that the screen is a little smaller and further away than you expected.