Text readability depends on mathematical relationships between font size, screen size, and display duration.

Minimum Font Size by Platform

Reading Speed Duration Formula

Average reading speed on mobile is 184 words per minute, or 3.1 words per second. Add 0.6 seconds per line as a buffer for viewer processing. For a two-line text overlay with 11 words, minimum duration is 4.1 seconds. This formula prevents the common error of three-second text displays that viewers report as too fast to read comfortably.

Contrast and Background Requirements

Text needs 4.5:1 contrast ratio minimum against backgrounds. White text requires backgrounds darker than RGB 118,118,118. Black text requires backgrounds lighter than RGB 137,137,137. Background blur at 24-32 pixel radius ensures readability over complex footage without completely obscuring underlying content.

Animation Timing Standards

Text fade-in and fade-out should not exceed 12 frames each at 30fps. Longer animations reduce actual reading time and frustrate viewers who want information quickly. Slide and scale animations work only when motion direction matches content flow, left-to-right for progressive information, right-to-left for retrospective or corrective statements.