Free tool · Video
Caption Reading Speed Checker (CPS and Line Length)
Netflix's English style guide allows up to 20 characters per second for adult programs, 17 for children's programs, 42 characters per line and two lines. The BBC recommends 160 to 180 words per minute and 37 characters per line. Paste SRT or VTT below to see every cue that breaks the standard you pick, with the measured number, and split long lines in one click.
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Up to 20 characters per second, 42 characters per line, 2 lines. Characters are counted with spaces.
Result
2 of 3 cues flagged.
Flagged cues
| Cue | CPS | Longest line | Lines | Problems |
|---|---|---|---|---|
| 1 | 31.5 | 63 | 1 |
|
| 3 | 16.04 | 77 | 1 |
|
Suggested splits only touch cues with a long line or too many lines, and break at the space nearest the middle, after punctuation where possible. Speed and duration problems need the text or timing edited by hand.
What characters per second is, and why it matters
Characters per second, usually shortened to CPS, is how many characters a viewer has to read each second a caption is on screen. Take the number of characters in the cue, divide by the seconds it is displayed, and you have the figure. A cue of 40 characters shown for 2 seconds is 20 CPS. The same text shown for 1 second is 40 CPS, and almost nobody can read that while also watching the picture.
It matters because captions compete with the video for attention. A viewer who is still reading the last line when the next one arrives stops looking at the picture, or gives up on the text. Fast cues are the commonest complaint about caption quality, and they are the one problem that cannot be fixed by formatting, because the only cures are fewer words or more time. The other measurable limits do a quieter job. A line that is too long runs past the safe area or wraps unpredictably. Three lines of text cover a large part of the frame. A cue that flashes for a fraction of a second is seen but not read, and one that stays for ten seconds feels stuck.
Counting rules differ and are worth knowing before you compare numbers. This tool counts every character in the cue, spaces included, and does not count the line break between two lines. Neither Netflix nor the BBC states in the pages linked below whether spaces are included in their figures, so that choice is ours, made so the result is easy to reproduce by hand. If you count differently, your numbers will be a little lower.
Two cues show the arithmetic. "Welcome back to the channel." is 28 characters, so at 2 seconds it is 14 CPS and comfortable under every limit here. "This is a fairly long caption line, that should split" is 53 characters, so at 2 seconds it is 26.5 CPS and over Netflix's adult limit by a wide margin, and at 53 characters on one line it is also over the 42 character line limit. Those are two separate problems with two separate fixes.
The published standards, side by side
Only two broadcasters publish enough detail to check against, and they do not agree. Every value below is transcribed from the publisher's own page, checked October 2026, with the page linked. Where a source gives no number, the cell says so rather than borrowing one.
| Rule | Netflix English, adult | Netflix English, children's | BBC |
|---|---|---|---|
| Reading speed | Up to 20 characters per second | Up to 17 characters per second | 160 to 180 words per minute (about 18 characters per second by our conversion) |
| Characters per line | 42 | 42 | 37, reduced if coloured text is used |
| Lines | 2 maximum | 2 maximum | 2 recommended for landscape or square video |
| Minimum duration | 5/6 of a second | 5/6 of a second | Around 0.3 seconds per word |
| Maximum duration | 7 seconds | 7 seconds | Not stated as a number |
Sources: Netflix English (USA) Timed Text Style Guide for reading speed, characters per line and lines; Netflix Timed Text Style Guide: General Requirements for duration; and the BBC Subtitle Guidelines for everything in the last column.
Two honest caveats. First, the BBC states reading speed in words per minute, so its characters per second figure here is our conversion, not a number the BBC publishes: 180 words per minute x 6 characters per word / 60 = 18, where the 6 characters per word is our assumption. The checker uses it only as a guide and says so. Second, these are deliverable specifications for two broadcasters, not laws. We did not research the limits of YouTube, TikTok or Instagram for this page, so we state none for them and invent none. Pick the standard closest to your audience and treat it as a good house style, not a requirement.
Why the two disagree is mostly about the audience and the screen. The BBC's figure is for subtitles sized to a region of the video; Netflix's is a delivery spec for a catalogue of dubbed and subtitled titles. The children's limit is lower because younger readers read more slowly. If you caption for a general web audience, 20 CPS and 42 characters is a workable ceiling, and 17 CPS is the safer choice when the audience skews young or reads in a second language.
How auto-captions break these rules
Speech recognition is good at the words and indifferent to how they are presented. A model returns segments, and a naive converter turns each segment into one cue. Nothing in that process knows about a 42 character line, a two line limit or a reader. A person asking for help with exactly this on the r/LocalLLaMA subreddit wrote that "The transcription text is great, but the subtitle splits are awful". That sentence is the whole problem: the transcript is fine, the segmentation is not.
- Long lines. A segment that ends at a pause in speech can be 80 or 100 characters, far past 42. The checker reports the longest line in each cue and the split button breaks it in two.
- Too many lines. A player that wraps a long single line can produce three or four lines on screen. The checker counts lines in the file, so a cue with line breaks already in it is measured as written.
- Fast cues. A quick speaker packs many words into a short segment. Splitting the text does not help, because splitting does not add time. The cue needs fewer words, a longer duration, or to be broken into two cues with their own times.
- Flashes. A one word segment can last a few hundred milliseconds, below the Netflix minimum of 5/6 of a second, and the checker flags it.
How the splitter chooses a break: it joins the text onto one line, then looks for the space nearest the middle, and prefers a space right after a comma, full stop or similar mark when that leaves both halves within the line limit and the shorter half at least a quarter of the text. If there is no punctuation it uses the nearest space to the middle that keeps both lines in the limit. Netflix's general requirements give the principle behind this: break lines after punctuation marks and before conjunctions and prepositions, and do not separate a noun from its article or a first name from a last name. The splitter implements the punctuation rule and the balance, not the grammar, so read the result.
For example, "This is a fairly long caption line, that should split" becomes "This is a fairly long caption line," on the first line and "that should split" on the second, because the comma is the nearest punctuation and both halves fit. Text with no space, such as a very long single word, is left alone because there is nowhere to break it.
Fixing a flagged cue
Each problem has its own cure, and choosing the wrong one wastes time. For a long line or a three line cue, press the split button. For a reading speed problem, there are three real options: cut words, give the cue more time by ending it later or starting it earlier if the neighbours allow, or split the text across two cues, each with its own timing. Netflix's English guide says when editing for reading speed to favour text reduction, deletion and condensing, and not to paraphrase, which is sound advice for any captioner.
For a duration problem, a cue below the minimum usually wants a longer end time, and a cue above 7 seconds under Netflix's rules usually wants to be broken into two cues. If you need to move whole files in time rather than adjust cues one at a time, convert and shift them with the SRT to VTT converter, which also lists malformed timestamps.
A last point on judgement. A checker can only compare numbers. A cue at 19.9 CPS with a hard word is harder to read than one at 22 CPS made of short common words, and an editor will sometimes accept a fast cue because the speaker is fast and the viewer expects it. Use the table to find the cues worth a second look, then decide with your own eyes.
How to check caption reading speed and line length
Step 1
Paste your captions or open a file
Paste SRT or VTT text, or press Open file. The file is read in your browser and never uploaded. The flagged count updates as you type.
Step 2
Choose a standard
Pick Netflix adult, Netflix children's or BBC. The limits for the choice are shown under the menu, and the table re-checks every cue at once.
Step 3
Read the flagged cues
Each row gives the cue number, its characters per second, its longest line, its line count and a plain statement of what broke, with the measured value next to the limit.
Step 4
Apply suggested splits and download
Press Apply suggested splits to re-break cues that have a long line or too many lines. Then download the SRT. Speed and duration problems are left for you to edit, because they need different words or different timing.
When you outgrow this tool
Linkeddit Studio caption styles set 1 to 12 words per line and 1 to 3 lines, burned into the video. It does not export SRT or VTT files.
This checker is free and complete on its own, with no account. Linkeddit Studio is the desktop editor for the video itself. It transcribes speech on your device with Whisper and burns the captions into the exported video, and its caption styles set 1 to 12 words per line and 1 to 3 lines. It does not export SRT or VTT files, so use this page to check a caption file that came from somewhere else. Studio is a one-time purchase.
FAQ
Caption Reading Speed Checker (CPS and Line Length) questions
Direct answers on characters per second, line length and caption timing.
What is a good reading speed for captions?
It depends on the standard you follow. Netflix's English style guide sets reading speed limits of up to 20 characters per second for adult programs and up to 17 for children's programs. The BBC recommends 160 to 180 words per minute. Those are two publishers' limits for their own delivery, not a law, so use the one that matches where the video will be shown.
How is characters per second calculated?
Count the characters in the cue, then divide by the number of seconds the cue is on screen. This tool counts every character on every line, spaces included, and does not count the line break. Netflix and the BBC do not say whether spaces count in their figures, so that rule is ours. A 40 character cue shown for 2 seconds is 20 characters per second.
What is the maximum characters per line for subtitles?
Netflix's English guide says 42 characters per line. The BBC's guidelines give 37 characters, reduced if coloured text is used, as the Teletext broadcast limit; for online video they constrain a line by the width of its subtitle region, 68% of the width of a landscape 16:9 video, and say that if you target both, the characters within a region must not exceed 37. Both allow two lines on landscape video, and the BBC suggests keeping to two lines.
How long should a subtitle stay on screen?
Netflix's general requirements give a minimum of 5/6 of a second per subtitle event (20 frames at 24 frames per second) and a maximum of 7 seconds. The BBC does not give a single minimum; it says to aim for around 0.3 seconds per word, so 1.2 seconds for a four word subtitle, and calls timing an editorial decision. This tool applies those two rules as written.
Can I convert words per minute to characters per second?
Only approximately, and the BBC states words per minute, not characters per second. The figure on this page for the BBC is a conversion, shown with its formula: 180 words per minute x 6 characters per word / 60 = 18. The 6 characters per word, an average English word of about 5 letters plus its trailing space, is our assumption. Real captions with long or short words will differ, so treat the BBC characters per second figure as a guide and the 180 words per minute as the source's number.
Why do my auto-generated captions fail the check?
Speech recognition decides where the words are, not how a reader should meet them. Splits often fall wherever the model's segment ends, so lines run long or stack into three lines, and quick speech packs too many characters into a short cue. The Apply suggested splits button fixes line length and line count. Fast cues need the text shortened or the timing changed.
Is my caption file uploaded?
No. The file is read in your browser, measured by plain JavaScript on your device, and any download is made in your browser as well. There is no account and no network request, so you can check unreleased material.
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