What is CPS (characters per second)?
Characters per second (CPS) measures how fast a caption has to be read: the number of characters in the block divided by the time it stays on screen. A 40-character caption that lasts 2 seconds runs at 20 CPS. The higher the number, the harder it is to read along with the speech.
Also called: CPS, reading speed
The same text at three durations
The caption “At my first one, I forgot the vows.” has 34 characters, counting spaces and punctuation. Screen time is what changes the CPS.
| Time on screen | CPS | Reading |
|---|---|---|
| 2.5 s | 13.6 | Comfortable |
| 1.7 s | 20.0 | At the common limit for English |
| 1.2 s | 28.3 | Too fast to read |
Why CPS matters
A caption that disappears before anyone reads it is worse than no caption at all. The common TV and streaming reference for adult audiences sits between 17 and 20 characters per second, and many English delivery specs use 20.
CPS also explains why translated captions take work: the translated text is often longer than the original in the same amount of time. It is also why good captions trim repetition without changing the meaning.
CPS in FilmScribe
We build captions from the timing of every word, and the SRT comes with TV, Netflix and YouTube presets. To check any SRT or VTT against streaming rules, use the free checker: it flags every block over the limit and suggests a fix.
Subtitle reading speed checker Paste your SRT and see the CPS of every block, the 42 characters per line, the duration and the gap between captions. Check my SRT →Keeping reading speed under control
- 01
Check duration, not only CPS
A one-word caption can have a low CPS and still flash past. Specs pair the CPS limit with a minimum time on screen, like Netflix's five sixths of a second, and a maximum of about seven seconds.
- 02
Respect the gap between captions
Many specs require a short gap between consecutive captions, often two frames, so the eye notices the change. When you extend a caption to lower its CPS, stop at that gap.
- 03
Never cut names, numbers or negatives
When you shorten text, drop repetition and false starts first. Names, numbers and small words like “not” and “never” stay, because losing them saves a few characters and changes the meaning.
- 04
Measure after the last edit
Check CPS on the final text, after translation, name fixes and new line breaks. A late swap of one word can push a block that passed over the limit.
Related terms
See all terms →Frequently asked questions
Do spaces and punctuation count toward CPS?
In most delivery specs, yes. The math uses every visible character in the block, including spaces and punctuation. Line breaks usually do not count.
What is a good CPS for English captions?
For adult audiences, 20 CPS is the most common streaming limit, with 17 in stricter guides. Children's content usually calls for much less. When in doubt, follow the spec of whoever receives the file.
How do I lower CPS without cutting the speech?
Extend the caption up to the start of the next one, split it into two blocks or trim repetition and filler words. The meaning has to stay the same.
Captions, clips and paper edits. All in one place.
Upload a video or paste a YouTube link. We transcribe every word with its timing, and you take the result to social media or to your editor.
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