Basic Research

Using the correct font sizes and font weights is necessary to define a document's structure and highlight the text. It helps to support the human eye to recognize a hierarchy of headings and focus on important information.

Whether a font size is readable depends on the distance between the reading surface and the eye. The further away the viewer is from the text, the larger the font must be. The specification of such a font size is measured in arc minutes as a relative size unit.

To be readable, text on a surface should be at least 10 vertical arc minutes away from the viewer's eye. However, if the minimum of 10 vertical arc minutes is used, eyestrain is likely over a longer time because the font is too small for most viewers. A safer rule of thumb is for any displayed text to occupy at least 15–20 arc minutes of the furthest viewer’s eyes.