What is the difference between readability and legibility?

Readability and legibility are two terms that are often used interchangeably, but they actually refer to different aspects of written communication.

Readability refers to how easy or difficult a piece of text is to understand or comprehend. It takes into account factors such as sentence structure, vocabulary, and organisation of ideas. A text with high readability is one that is clear, concise, and easy to follow. Readability is often measured using formulas like the Flesch-Kincaid Readability Score, which considers factors like the number of syllables per word and the length of sentences to assign a reading level to a piece of text.

Legibility, on the other hand, refers to how easy or difficult it is to physically read the text. It takes into account factors such as font choice, font size, spacing, and contrast between the text and the background. A text with high legibility is one that is easy on the eyes, and can be read comfortably for extended periods of time without causing eye strain or fatigue.