Reading speed on this site is the words-per-minute version of the same job. CPS is the character version, and it travels better across languages because word length is not stable: English, German and a CJK glyph do not contain the same amount of meaning per token. The formula is dull on purpose. Count the characters in the cue, including spaces, and divide by how many seconds the cue stays up. A 51-character line up for three seconds is 17 CPS. Stretch it to one second and the same line is 51, which the eye will not finish.
Streaming and broadcast houses publish caps in this unit because the file formats do not. A cue that matches the mouth 1:1 with a fast talker will flash. Caption line length is the other lever: a 90-character block at a legal CPS is still a paragraph on a 9:16 frame. Fix the shape first (split at a clause, two lines), then check that the duration matches the count. Caption timing is when the cue appears; CPS is whether a person can read it before it leaves.
Auto captions will happily emit both failures at once — a long line, and a short dwell — because the speaker did not pause. That is an editorial pass, not a punchier preset. Watch the cut on mute at phone size. If you cannot finish the line, the CPS is too high, whatever a desktop preview suggested.
In practice
- Compute CPS as characters including spaces, divided by on-screen seconds — not as a vibe about how fast the voice feels.
- Split the cue or hold the out-point before you shrink the type. Small letters at 30 CPS are still unreadable.
- Compare Latin-script CPS only to Latin-script caps. A CJK glyph is a different unit.
The mistake to avoid
Treating WPM and CPS as interchangeable scores. Five characters per word is a teleprompter convention, not a measurement of the cue in front of you.
Where you will run into it
- Add Captions to a Video — Speech in, styled subtitles out — no manual timing.
- AI Caption Generator — Drop a video, get timed captions. Free, on your device, no upload.
Related terms
Reading speed
Caption reading speed is how fast on-screen words arrive, in words per minute. A cue gone before it can be read is a timing error, not a style one.
Caption line length
Caption line length is how many characters sit on one cue. Latin-script lines are commonly kept near 42 characters so a phone can still read them.
Caption timing
Caption timing is when each line appears and disappears relative to the speech — the clock, not the words and not the look.
Hook rate
Hook rate meaning: the share of people shown a video who are still watching a few seconds in. It grades the opening, not the body.
Retention curve
Retention curve meaning: how many starters are still watching at each second. Watch time is the area under that curve.
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