1. Point Size 

But there’s more to that. Thing is, not all fonts are the same. At the same point size different fonts can still appear to be of a different size.

To see the difference try using the simple, but powerful squint method: squint your eyes and compare the overall size and contrast of every paragraph. 

It is better to see for yourself which point size for a particular font you want to use. Don’t be afraid to go a bit smaller than the 12 points/25 pixels suggestion.

The majority of books, newspapers and informative flyer printing have a point size smaller than 12, and it usually works fine. 

However, when considering a font size for on-screen viewing, feel free to make it a bit bigger, as the monitors are usually at a further distance from our eyes than the books. Exceptions are, of course, the phones as they are viewed arm-length away. 

2. To Black or Not To Black 

The screens have a strong backlight and the black-white contrast created by pure black text can be tiring on eyes. There is some debate on this going on, but it seems to be the choice which caught on among the general public.

The Material Design guidelines also set the standard for the body text to be between 87% and 54% opacity. 

For print, though, the conditions of how the text is read are different. The light is unequally distributed, and there is generally less control of the environment in which it will be seen. That’s why it is important to provide maximum possible contrast.