Fifty across — the optimal font size

As long as text remains the main component on presentation slides legibility will be one of the main factors to consider when it comes to designing our visuals. Since the invention of movable type printing, about 570 years ago, typographers, typesetters, and graphic designers had plenty of time to figure out how to improve the legibility of text. As a rule of thumb, the optimal legibility of printed continuous text lies between 60 and 80 characters per line. But, how about text projected on a screen?

Books are usually being read from a distance shorter than an average arm’s length. That gives the designer the opportunity to optimize text legibility. When designing a poster those conditions change and the font size has to be increased according to the average reading distance — the bigger the distance the bigger the font size. It gets far more complicated when it comes to presentation design. Not only are there different slide sizes, data projectors offer different resolutions, the size of projection screens can vary considerably, as can the distance between our listeners and the screen. We have to consider all possible circumstances. The general rule for font size is: the bigger the better.


“Fifty zeros across” is a simple way to define the minimal font size despite all the different factors involved. We create a new text box that stretches across the whole slide and fill that box with 60 zeros of the font of our choice (starting with ten zeros, colouring the last one red, copying & pasting the rest). Then we increase the font size of the zeros until fifty zeros (or slightly more) fill the line from border to border. Our example slide is 720 x 540 pixels of size, the font is Arial, starting at 12 point. We increase the font size until we arrive at about 50 zeros across. The resulting font size should be a round number. We settle at 24 point for our minimal font size.

The minimal font size is being used for labels in graphs, charts, diagrams, tables, etc. The optimal font size should be 50% bigger than that, in our case 36 point. Headlines can be double the optimal font size.

Axel Wendelberger