Caption and subtitle checker
Paste or open an .srt or .vtt file and check every caption against Netflix, BBC or DCMP limits: reading speed, line length, lines, time on screen, gaps and overlaps.
- Free, no sign-up
- Your file never leaves your browser
- Limits from Netflix, the BBC and DCMP
Caption standards side by side
Netflix allows up to 20 characters a second and 42 characters a line for English subtitles, the BBC recommends 160–180 words a minute, and the DCMP Captioning Key caps educational captions at 130–160 words a minute. Each limit below is taken from the standard's own page, read on October 15, 2026.
| Netflix (English) | BBC | DCMP Captioning Key | |
|---|---|---|---|
| Reading speed | Up to 20 characters a second (adult programs), 17 (children’s programs) | 160–180 words a minute, or 0.33–0.375 seconds a word | Up to 130, 140 or 160 words a minute for lower-, middle- and upper-level educational media |
| Characters a line | 42 | 37 on broadcast (Teletext); online, a share of the screen width (68% of a 16:9 video) | No character count; captions must stay within reasonable margins |
| Lines a caption | Two at most; usually one unless the text exceeds 42 characters | Two for 16:9, 4:3 or 1:1 video; three for vertical 9:16 video | No more than two preferred; three or four only to avoid graphics |
| Shortest time on screen | 5/6 of a second (20 frames at 24 fps) | About 0.3 seconds a word (1.2 seconds for 4 words) | 40 frames (1 second and 10 frames) |
| Longest time on screen | 7 seconds | No number; end the caption with the speech, since captions left on too long get re-read | 6 seconds (background music notes excepted) |
| Gap between captions | 2 frames minimum at any frame rate; gaps under half a second are closed to 2 frames | If you leave a gap for a pause, at least 1 second (preferably 1.5) | No rule |
How the checker counts
Characters include letters, spaces and punctuation on every line, but not line breaks or formatting such as <i> tags and {\an8} position codes. Reading speed is characters ÷ seconds on screen (out-time minus in-time), and words a minute counts any run of characters that holds a letter or a digit, so speaker labels and sound tags count, as DCMP asks. Gaps run from one caption's out-time to the next caption's in-time, in frames at the frame rate you pick. A caption that breaks a limit is flagged; advice that a standard words as a recommendation (the BBC's 0.3 seconds a word, its one-second gaps, Netflix's half-second chaining, DCMP's two-line preference) is shown separately.
Fixing what it flags
Too fast: cut words before you cut time. Netflix's guide says to favor text reduction, deletion and condensing
when editing for reading speed; then use any gap to start the caption earlier or end it later. Lines too long: break at a natural point, never after a conjunction or between an auxiliary verb and its verb, as the DCMP Captioning Key puts it. Gaps and overlaps: for Netflix, set each out-time two frames before the next in-time wherever the gap is under half a second. Our guide to burned-in vs closed captions has the caption spec we hand every editor, and the video captions statistics page has the numbers on who uses captions and why.
Sources: Netflix English (USA) Timed Text Style Guide · Netflix Timed Text Style Guide: General Requirements · Netflix Timed Text Style Guide: Subtitle Timing Guidelines · BBC Subtitle Guidelines · DCMP Captioning Key: Text · DCMP Captioning Key: Presentation Rate, read on October 15, 2026.
Embed this calculator
Teachers, bloggers and course creators can put this caption checker on their own page for free. Paste the code below into your page's HTML. It loads from markstudios.com, so it stays current when we update the numbers.
Questions, answered.
Anything else? Message Mark and you'll get a written reply within one business day.
What is a good reading speed for subtitles?
Netflix’s English style guide allows up to 20 characters per second for adult programs and 17 for children’s programs. The BBC subtitle guidelines recommend 160–180 words per minute, or 0.33 to 0.375 seconds per word. The DCMP Captioning Key, written for educational media, caps captions at 130 words per minute for lower-level, 140 for middle-level and 160 for upper-level material.
How many characters per line should a subtitle have?
Netflix allows 42 characters per line for English subtitles. The BBC’s limit is 37 characters on broadcast platforms that use Teletext; online it sets a share of the screen width instead (68% of a 16:9 video). The DCMP Captioning Key gives no character count and asks for captions within reasonable margins.
How long should a subtitle stay on screen?
Netflix sets a minimum of 5/6 of a second (20 frames at 24 fps) and a maximum of 7 seconds per subtitle. The DCMP Captioning Key sets a minimum of 40 frames (1 second and 10 frames) and a maximum of 6 seconds. The BBC aims for about 0.3 seconds per word, so 1.2 seconds for a 4-word subtitle.
How many lines can a caption have?
Two at most for Netflix, which keeps text to one line unless it exceeds 42 characters. The BBC recommends two lines for landscape or square video and three for vertical 9:16 video. The DCMP Captioning Key prefers no more than two.
What gap should there be between subtitles?
Netflix’s timing guidelines keep a minimum gap of 2 frames at every frame rate and close any gap shorter than half a second to 2 frames. The BBC says that if you leave a gap for a pause, it should be at least one second, preferably a second and a half.
How do I fix subtitles that are too fast to read?
Netflix’s guide says to favor text reduction, deletion and condensing when editing for reading speed. You can also start the caption a little earlier or end it later if there is a gap, or split a long caption into two. The DCMP Captioning Key suggests borrowing 15 frames before or after the audio.
Does the checker upload my caption file?
No. The file is read and checked in your browser and never leaves your device. You can also paste the captions in as text.
Which caption files does it read?
SubRip (.srt) and WebVTT (.vtt). Formatting such as <i> tags or {\an8} position codes is ignored when characters are counted, and WebVTT NOTE, STYLE and REGION blocks are skipped.
Rather have captions done for you?
Captions are timed and checked as part of every edit: send the footage through the instant quote for a written price, and you work directly with Mark.
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