How to Review Subtitle Readability

A technically valid file can still be hard to read. Readability review checks whether viewers can comfortably read each subtitle in the time it's on screen.

Line length

Keep lines to about 42 characters or fewer. Shorter lines are easier to read and less likely to wrap on small screens.

Lines per cue

Use at most two lines per cue.

Reading speed

Reading speed is measured in characters per second (CPS):

CPS = characters in the cue ÷ seconds on screen

Common guidance ranges from about 15 CPS (for broad audiences and learners) to 20 CPS. A 60-character cue therefore needs roughly 3–4 seconds.

Display time

Avoid cues shorter than about 5/6 of a second — they flash by — and longer than about 7 seconds, after which viewers tend to re-read.

Line breaks

Break lines at natural linguistic boundaries. Avoid separating:

• an article from its noun ("the / report"),
• a preposition from its object,
• a first name from a surname.

✗ Please review the                    ✓ Please review
  quarterly report before Friday.        the quarterly report before Friday.

When rules conflict

Fast speech sometimes makes it impossible to meet reading-speed rules without condensing text. Condensing changes the words, so it should only happen with the content owner's approval.