# How to determine if the font on your slides is big enough; Issue #152 February 5, 2008

PowerPoint Tip: Is Your Font Big Enough?

One of the questions that comes up often in my workshops is “How big of a font should I use?” The answer is … It depends.

You certainly don’t want to do what I have seen twice in the past 18 months. These two presentations have set the record for smallest font used on a slide in my experience. They used a five point font. No, that is not a typo. Five (5) point! And they expected the audience to be able to read it.

So how do I answer the font size question? I did the research to come up with a way that I could determine an appropriate font size.

I started by considering visual acuity. This is the term used for how well we see. It is what the optometrist measures using the eye chart that starts with the large “E” at the top and smaller lines below. They determine your visual acuity based on how tall a letter you can clearly see at what distance. It is important that we have the letters on our slides large enough so most people can see them. But the next challenge was to figure out what level of visual acuity I should assume for most audiences.

To answer the average vision question I turned to the standard they use for road signs in North America. There is a manual for designers of road signs that specify how big the letters should be in order for the text to be read at a certain distance from the sign. So I used these standards and the visual acuity measurement standards to determine that road signs assume approximately 20/35 vision (20/20 is perfect vision). So, to be conservative, I assume 20/40 vision (it is also one of the standard measurements).

I then used a projector to calculate the ratio of height of a standard Arial font to the width of the projected image. This allows me to know how tall a letter of a particular point size will be on a screen of a certain size.

Now I had all the parts I needed. Using the assumptions of 20/40 vision and that the image fills the screen, I could calculate the maximum distance that an audience member should be to comfortably read a font of a certain size. Now I can answer the font size question based on research, not on a feeling. There is no one single answer, it depends on screen size and the distance of the furthest person in the room.