Measure characters per line, CPS and WPM for one subtitle or a whole SRT or WebVTT file, and see which cues break the limits.
This tool runs entirely in your browser. What you enter is never sent anywhere.Your input is never sent anywhere.
DetailsLimits to check against
Subtitle text
Result (Netflix (adult))
Characters per line
Suggested on-screen time
At least 2.1 s (maximum 7 s)
Based on the Netflix (adult) limits: 20 CPS limit · 0.83 s minimum
Timing is within this preset's limits
Reference only
The presets follow published guidelines for English subtitles. Your client or platform decides what counts as acceptable, so check their current style guide before delivery.
What this subtitle checker measures
A subtitle can be well written and still fail if viewers cannot finish reading it before it disappears. For each cue, this tool measures characters per line, number of lines, and reading speed for the time the cue is on screen.
Pick a preset (Netflix adult, Netflix children, or BBC) or enter your own limits, then type one subtitle or paste a full SRT or WebVTT file. Every cue that breaks a limit is flagged with the reason, so you can fix the fastest ones first.
Reading speed is shown as characters per second (CPS) and words per minute (WPM). Netflix states its limits in CPS and the BBC states its recommendation in WPM, so the presets check whichever one the guide uses.
Where a subtitle check helps
Quality check before you send the file
Run your SRT through the checker before it goes to a client or a platform. You get a list of cues to fix instead of finding them in a reviewer's notes.
Cleaning up auto-generated captions
Speech-to-text captions often come out with long lines and cues that flash by. Paste the export and filter to problem cues to see where to re-time or reword.
Reviewing a translator's or freelancer's file
Check delivered subtitles against the same limits every time, without stepping through the file cue by cue in your editor.
Testing your own house rules
If your team uses its own line length or speed limit, set it in Custom and run the same file against it. Enter 0 for any limit you do not want checked.
Check one cue or a whole SRT file in 4 steps
- Choose Single subtitle to test one cue, or SRT / VTT text to test a whole file.
- Pick a preset (Netflix adult, Netflix children, BBC), or choose Custom and enter your own limits.
- Type the subtitle and its on-screen time in seconds, or paste your SRT or WebVTT text.
- Read the result. Edit the text or timing, and the results update as you type.
Note: Everything runs in your browser. The text you enter is not uploaded.
Limits of this check
- The presets are based on the Netflix English Timed Text Style Guide and the BBC Subtitle Guidelines. Both are revised from time to time, so confirm the current numbers with your client or platform before delivery.
- Passing this check does not mean a platform will accept your file. Delivery specs also cover file format, gaps between cues, allowed characters and more, and none of those are checked here.
- Characters are counted including spaces. Text between < and > and codes like {\an8} are ignored, and blank lines are skipped.
- WPM is the number of space-separated words divided by the on-screen time. The Netflix presets check CPS only and the BBC preset checks WPM only. Custom checks whichever limits you set above 0.
- Line breaks are not judged. The tool counts lines and characters but cannot tell whether a break falls at a natural phrase boundary.
- This tool is not affiliated with Netflix or the BBC.
Netflix vs. BBC subtitle limits at a glance
The limits built into the presets. Published guides are revised, so treat these as reference values.
| Preset | Max characters per line | Max lines | On-screen time | Reading speed limit |
|---|---|---|---|---|
| Netflix (adult) | 42 | 2 | 5/6 s to 7 s | 20 CPS |
| Netflix (children) | 42 | 2 | 5/6 s to 7 s | 17 CPS |
| BBC | 37 | 2 | Not checked | 180 WPM (BBC recommends 160 to 180) |
| Custom | You set it | You set it | You set it | You set it |
CPS, WPM and line breaks: what to fix first
How the measurements relate, and what to change when a cue is flagged.
CPS and WPM measure the same thing in different units
CPS divides the characters in a cue by its on-screen seconds. WPM divides the words by its on-screen minutes.
Long words cost more in CPS than in WPM, so a cue can pass one and fail the other. Check against the unit your client or platform names.
Line length: 42 characters or 37
Netflix allows 42 characters per line in English, and the BBC guidelines use 37. Both allow two lines per subtitle.
A line over the limit may wrap or get cut off on some players, so shorten it or move part of it to the second line.
Fixing a cue that reads too fast
There are three ways to bring CPS or WPM down: extend the out time if the next cue starts later, shorten the text, or split the cue in two.
A cue also should not stay up longer than the maximum, which is 7 seconds in the Netflix presets, so a long pause is better handled by splitting.
Breaking a subtitle into two lines
Where you can, break after punctuation or before a conjunction or preposition so each line reads as a phrase.
This tool checks only the length and number of lines. You still need to read the cue to judge whether the break is natural.
Common subtitle timing and line-break mistakes
Every line passes, but the cue still reads too fast
Two lines of 40 characters are within the line limit, but if the cue is on screen for only 2 seconds, the speed is 40 CPS.
💡 See the solution▼
Single words that flash by
A one-word reply timed to the audio can be on screen for well under a second, which is shorter than the 5/6 second minimum in the Netflix presets.
💡 See the solution▼
Checking against the wrong preset
A file that passes Netflix (adult) at 42 characters and 20 CPS can fail the Netflix children preset at 17 CPS, or the BBC preset at 37 characters.
💡 See the solution▼
Splitting a line only to meet the character limit
Breaking a sentence at a random point gets the line under the limit, but the viewer has to rejoin the pieces while reading.
💡 See the solution▼
Questions about CPS, WPM and SRT files
Q.How many characters per line should a subtitle have?
A. The Netflix English style guide allows up to 42 characters per line, and the BBC Subtitle Guidelines use 37. Both allow two lines per subtitle. This tool counts every character on a line, spaces included, and flags any line above the limit of the preset you picked.
Q.What does CPS mean in subtitles, and how is it calculated?
A. CPS is characters per second: the number of characters in a subtitle (spaces included) divided by the seconds it stays on screen. A 40-character subtitle shown for 2 seconds runs at 20 CPS. The higher the number, the faster the viewer has to read.
Q.What is a good subtitle reading speed?
A. Netflix sets a ceiling of 20 CPS for adult English programs and 17 CPS for children's programs. The BBC recommends 160 to 180 words per minute (WPM). If a cue is over the limit, give it more time, shorten the text, or split it into two cues.
Q.How long should a subtitle stay on screen?
A. Netflix sets a minimum of 5/6 of a second and a maximum of 7 seconds per subtitle. The BBC suggests roughly 0.3 seconds per word. The Suggested on-screen time box shows the shortest time that satisfies the limits of your selected preset for the text you entered.
Q.Can I check an SRT or VTT file?
A. Yes. Open the SRT / VTT text mode and paste the contents of the file. The checker reads each timing line, measures every cue, and lists the ones that break a limit. You can turn on Problem cues only to hide the cues that pass. It reads pasted text, so open the file in a text editor and copy its contents.
Q.Are formatting tags like <i> counted as characters?
A. No. Anything between < and > on a line, and codes in the form {\an8}, are removed before counting. Blank lines are skipped and do not count toward the line limit.
Q.Is my subtitle text uploaded anywhere?
A. No. The checks run in your browser, and the text you type or paste is not sent to this site's server. Closing or reloading the page clears it.
Q.Does passing this check mean Netflix or the BBC will accept my subtitles?
A. No. Delivery specs cover more than line length and reading speed, such as file format, gaps between cues and allowed characters, and this tool does not check those. Use it as a self-check on the draft, and follow the current style guide from your client or platform. This tool is not affiliated with Netflix or the BBC.
Q.Can I use it for subtitles in languages other than English?
A. You can, with the Custom preset. The Netflix and BBC presets are based on English guidelines, and other languages have their own limits. The tool counts each character as one, so enter the limits that apply to your language.
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