Subtitle reading speed: what CPS means and how to fix fast subtitles
In short: reading speed is how many characters a viewer has to read per second while a subtitle is on screen, written as CPS. Netflix allows up to 20 CPS for adult English programmes and 17 CPS for children's. The BBC measures in words per minute and recommends 160 to 180. A subtitle that reads too fast needs more time on screen, fewer words, or to be split in two.
What is subtitle reading speed?
Subtitle reading speed is the number of characters in a subtitle divided by the number of seconds it stays on screen. It is usually written as CPS, characters per second. A subtitle with 42 characters that is on screen for 2 seconds reads at 21 CPS.
The higher the number, the less time the viewer has to finish reading before the subtitle disappears. Above the limit, viewers either miss words or stop watching the picture to keep up.
Some guidelines, including the BBC's, measure speed in words per minute (WPM) instead. There is no exact conversion between the two, because it depends on how long the words are.
What reading speed limits do Netflix and the BBC use?
Netflix sets a maximum of 20 characters per second for adult English programmes and 17 for children's programmes. The BBC recommends 160 to 180 words per minute, and about 0.3 seconds per word as a target minimum time on screen.
| Source | Reading speed | Other timing limits |
|---|---|---|
| Netflix, English (USA) Timed Text Style Guide | 20 CPS adult 17 CPS children | Each subtitle on screen for at least 5/6 of a second and at most 7 seconds. |
| BBC Subtitle Guidelines (version 1.2.5) | 160 to 180 WPM | About 0.3 seconds per word as a minimum, for example 1.2 seconds for a four-word subtitle. Timing stays an editorial decision. |
Netflix publishes separate guides for other languages, with their own limits. If you deliver in another language, check the guide for that language.
Subtidy's presets use these numbers as a starting point. The Streaming preset matches the Netflix English adult limits. Subtidy is not affiliated with Netflix or the BBC.
| Subtidy preset | Reading speed | Time on screen | Try it |
|---|---|---|---|
| Streaming | 20 CPS | 0.83 s to 7 s | Open with Streaming |
| Broadcast | 15 CPS | 1 s to 6 s | Open with Broadcast |
| Social vertical | 17 CPS | 0.7 s to 4 s | Open with Social vertical |
Custom limits for a client's own spec, such as 17 CPS for a broadcaster, are part of Subtidy Pro.
How do you calculate CPS?
Count the characters in the subtitle, then divide by its duration in seconds. The duration is the out time minus the in time. Take this cue:
14
00:01:02,300 --> 00:01:04,100
I told you we'd be late,
and now look at us.The first line has 24 characters and the second has 19, so 43 in total. It is on screen for 1.8 seconds. 43 divided by 1.8 is 23.9 CPS, which is over a 20 CPS limit. To pass at 20 CPS it needs at least 2.15 seconds on screen, and at 17 CPS it needs 2.53 seconds.
Tools count slightly differently. Subtidy counts every visible character, including spaces and punctuation, and ignores line breaks and formatting tags such as <i>. Some tools leave out spaces. If a client's QC flags cues that your tool passes, ask how they count.
CPS calculator
Paste a subtitle and its timings. This uses the same counting as the Subtidy workspace.
Why do subtitles end up reading too fast?
Most fast subtitles come from text that was never edited to fit the time available. The usual causes:
- Verbatim transcripts of fast speech. Every word is kept, so the text outruns the time the speaker takes to say it.
- Automatic transcription. Speech-to-text tools cut subtitles where the speaker pauses, not where a viewer needs more time, so one cue can hold a whole sentence.
- Translation. Translated text often runs longer than the source, while the timing stays the same.
- Timing squeezed by neighbours. Closing an overlap or keeping a gap trims the end of a cue, which raises its speed.
- Frame rate changes. Speeding a programme up from 23.976 to 25 fps makes every subtitle about 4% shorter. See frame rate conversion.
How do you fix a subtitle that reads too fast?
Give it more time, give it fewer characters, or split it into two subtitles. In practice, try them in this order:
- Extend the out time into the free time before the next subtitle, keeping the minimum gap your spec asks for.
- Start it a little earlier if there is free time before it. Be careful here: Netflix and the BBC both want subtitles to appear with the start of speech.
- Split it into two subtitles when there is enough total time but too much text for one.
- Condense the text when there is simply not enough time. This is an editorial job: keep the meaning and the speaker's voice, drop repetition and filler.
How Subtidy fixes reading speed automatically
Subtidy applies the first three fixes to every cue in the file at once and leaves the fourth to you.
- Cues that read too fast, or sit on screen too briefly, are extended into the free time after them, up to the next subtitle minus the minimum gap.
- If that is not enough, Subtidy can start the cue up to 300 ms earlier when there is free time before it. If your spec wants subtitles to start exactly on the first frame of speech, check those cues.
- Cues that need more lines than the preset allows are split into consecutive subtitles, with the time shared out by the length of each part.
- Subtidy never rewrites your words. Cues that are still too fast after timing fixes stay flagged as Reads too fast. Turn on Only problems in the cue list to find them.
The QC report shows how many cues read too fast before and after, so you can see what changed and what still needs an edit.
Fix reading speed in your file
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Sources
- Netflix Partner Help Center, English (USA) Timed Text Style Guide, updated 19 December 2025.
- Netflix Partner Help Center, Timed Text Style Guide: General Requirements.
- BBC, Subtitle Guidelines, version 1.2.5, March 2026, section 4 Timing.