Subtitle line length and CPS checker
Every line is measured for characters per line, number of lines, reading speed and time on screen, against limits you set. Lines that fail are listed and can be fixed.
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.srt .vtt .ass .ssa .sbv
Drop a subtitle file here
Drop the video too to preview the lines over it and to set each start and end by its sound. Nothing is uploaded. No subtitle yet? Make one from the audio with transcribe.tools.
Formats it reads and writes
| Format | Timecode | Kept when saved here |
|---|---|---|
| SRT.srt | 00:01:23,450 | Italic, bold, underline, font tags |
| WebVTT.vtt | 00:01:23.450 | Italic, bold, underline |
| ASS.ass .ssa | 0:01:23.45 | Styles, actors, {\an8} and {\pos} when the file was ASS |
| SBV.sbv | 0:01:23.450 | Text only |
Reading speed and timing limits
The presets of the checker: Netflix English. Every number can be changed.
| Limit | Adult | Children’s |
|---|---|---|
| Characters per line | 42 | 42 |
| Lines per subtitle | 2 | 2 |
| Reading speed, CPS | 20 | 17 |
| Shortest on screen | 833 ms | 833 ms |
| Longest on screen | 7 s | 7 s |
| Gap between lines (2 frames at 24 fps) | 83 ms | 83 ms |
Source: Netflix Partner Help Center, English (USA) Timed Text Style Guide; Netflix Partner Help Center, Timed Text Style Guide: General Requirements; Netflix Partner Help Center, Timed Text Style Guide: Subtitle Timing Guidelines, opened .
How to use the line length and cps
- 00:01
Choose the limits
Use your client’s numbers, or start from the Netflix English presets linked in the panel.
- 00:02
Read the list
Every line outside a limit is listed with the measured value. Click one to jump to it.
- 00:03
Fix and save
Close overlaps and rewrap long lines in one step, preview the time each fast line can be given, then fix the rest by hand.
What is CPS in subtitles?
Characters per second: how many characters a viewer has to read in the time a line is on screen. A line of 40 characters shown for 2 seconds is 20 CPS. It is the usual measure of whether a subtitle is readable, because a viewer also has to watch the picture. This checker counts the characters a viewer sees, including spaces and punctuation, without formatting tags or the line break.
What limits should I use?
The one your client, broadcaster or platform asks for. If you have none, Netflix publishes its own for English: up to 42 characters per line, a maximum of two lines, and up to 20 characters per second for adult programs or 17 for children’s programs. Its general requirements add a minimum of 5/6 of a second and a maximum of 7 seconds per subtitle, and its timing guide a minimum of 2 frames between subtitles. Those are the two presets here, linked to the pages they come from; every number can be changed.
How are lines that are too long fixed?
Rewrap long lines breaks a line into at most the number of lines you allow, each within the limit. With two lines, it picks the break that keeps the longer line shortest, prefers a break after punctuation and, when two breaks are equal, leaves the bottom line longer, the “bottom-heavy” shape style guides prefer. A line whose words cannot fit is left as it was and stays in the list for you to shorten by hand.
How is a reading speed that is too high fixed?
Either give the line more time or use fewer words. The Reading speed section of the Check panel does the first and shows the result before you apply it: for every line over the limit it lists the CPS before and after and the new end time. A line grows at its end into the free time before the next one, keeping your minimum gap and never going past your longest duration. An option also takes up to 0.3 s from the start of the next line, but only when that line can spare it and still read within the limit. Another option, off by default, joins a line that is still too fast with the line after it, as one subtitle of two lines shown from the start of the fast line. A pair is joined only when both lines still fit your limits for line length, number of lines and duration, and the joined subtitle reads within the limit; the next line then appears with the fast one. The preview lists the joined text and its new times. A line that no free time or join can fix is listed with the number of characters to cut, or the seconds it would need on screen; shorten the text in the editor and the CPS badge updates as you type.
Questions
Are spaces counted?
Yes, spaces and punctuation are counted, which is how most subtitling tools measure CPS. Formatting tags and the line break between two lines are not.
Why does the checker flag small gaps?
Two lines with only a few milliseconds between them look like a flicker. The gap check flags anything under your minimum gap, and Close overlaps and gaps moves the end of the earlier line back to make room.
Is 42 characters per line a universal rule?
No. It is Netflix’s number for English. Other broadcasters, languages and screen sizes use other limits, which is why every limit here is a field you can change.
Can I see the CPS of each line?
Yes. Every row of the list shows its reading speed, and rows over your limit are marked. The issue list jumps to a line when you click it.
Does checking change my file?
No. Checking only measures. The file changes when you apply a fix, and Undo takes it back.
Does the reading-speed fix change my words?
No. The words of every line stay exactly as they were. The fix moves times: the end of a line and, with the options on, the start of the next one. A joined pair is one subtitle with both texts, one under the other. A line that cannot be fixed by time or a join is left for you to shorten.
Why does splitting a line not fix its reading speed?
Splitting does not lower it. Two parts shown one after the other need the same total time at the same limit, and line breaks are not counted, so the reading speed of the whole does not change. The Split button in the editor shares the time between the two parts in proportion to their length, which keeps each part at the same reading speed. What lowers it is more time on screen, a join with a line that has time to spare, or fewer characters.
More subtitle tools
- Subtitle editorEdit lines over your video, then save as SRT, VTT, ASS or SBV.
- SRT to VTTWebVTT for HTML5 players, with header and timestamps rewritten.
- Shift timingMove every line earlier or later, or only from a point on.
- Fix syncTwo-point resync and frame-rate change for drifting subtitles.
- ASS to SRTPlain SRT from ASS or SSA, with italics and line breaks kept.
- Merge and splitJoin two parts, combine two languages, or cut a file in two.
Sources
- English (USA) Timed Text Style Guide
42 characters per line, maximum two lines, up to 20 characters per second for adult programs and 17 for children’s programs, and where to break a line.
Netflix Partner Help Center. Opened on .
- Timed Text Style Guide: General Requirements
Minimum duration of 5/6 of a second per subtitle event (20 frames at 24 fps) and maximum duration of 7 seconds.
Netflix Partner Help Center. Opened on .
- Timed Text Style Guide: Subtitle Timing Guidelines
Subtitles must have a minimum of 2 frames between them, at any frame rate; gaps should be either 2 frames or half a second or more.
Netflix Partner Help Center. Opened on .
Style limits differ between broadcasters, languages and clients; the presets are one published guide, and every limit can be changed. Your files never leave your browser.