The problem with point size

“What’s the smallest point size you can put on a poster?”

This is a common question, but it’s not one that has a simple answer.

I know many scientists read this blog, and scientists work in a world where measurements are universal. 37°C is 37°C no matter wherever you are, whatever you’re measuring, and are exactly comparable. Someone from a scientific background probably thinks that two identical pieces of text – in different fonts but the same point size – should take up the same space.

I have bad news. Point size does not work like that.

These two paragraphs are both set in serif typefaces, both nominally 16 points in size, but one takes 19% more column length than the other. This difference can arise because individual letters in the two fonts might have the same height, but different widths. The letter O may be a wider circle, or a narrower oval, for example.

That 19% will make a big difference in your layout, even if the two blocks of text are similarly readable.

I have selected two fonts with a fairly large difference here. Many other standard fonts will probably be more similar in their use of space. But it points out that you can’t rely on font size alone to guide your poster design.

Instead of blindly following a minimum font size, work from a couple of guiding principles.

1. The bigger the text, the better.
2. Test, test, and test some more. Print full sized sample paragraphs at the point size you want to use (12 point 18 point, 24 point, 30 point), tack them to a wall, and stand back a couple of meters and see how they look.

But if all thoughtful design and testing stuff bores you, the answer is:

Nothing smaller than 24 point on your poster.

There. Happy?