Subtitle Guidelines: The Rules Netflix, BBC and Prime Video Follow
Professional subtitle guidelines agree on the shape: one or two lines, about 42 characters a line, a reading speed viewers can keep up with, and each subtitle on screen for roughly 1 to 7 seconds. The exact numbers differ by platform. Open an SRT or VTT file and every line outside the common limits is flagged.
Check subtitles against the rules
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Subtitle Rules Compared: Netflix, BBC and Prime Video
Three public style guides, side by side. Netflix and Prime Video write delivery requirements for the files they accept; the BBC guidelines are recommendations for its own programmes. Each counts some rules differently, so compare like with like.
| Rule | Netflix (English, USA) | BBC | Prime Video | What the check flags |
|---|---|---|---|---|
| Lines per subtitle | Two at most | Two recommended; three for vertical 9:16 video | Two at most, and one line when the text fits | More than 2 lines |
| Characters per line | 42 | 37 on broadcast; online, up to 68% of the width of a 16:9 frame | 42 | A line over 42 characters, spaces included, formatting tags not counted |
| Reading speed | Up to 20 characters per second; 17 for children’s programmes | 160–180 words per minute | Up to 17 characters per second; 13 for children’s programmes | Over 20 characters per second |
| Shortest time on screen | 5/6 of a second (20 frames at 24 fps) | No fixed minimum; about 0.3 seconds per word as a guide | About 5/6 of a second | Under 0.83 seconds |
| Longest time on screen | 7 seconds | — | 7 seconds | Over 7 seconds |
| Gap between subtitles | At least 2 frames | When there is a pause in speech: at least 1 second, ideally 1.5 | At least 2 frames | Not checked; overlapping subtitles are flagged as a warning |
| Shot changes | Start on the first frame of the shot; end 2 frames before the cut | Avoid subtitles that run across a shot change | Snap to a cut within 3 frames; end 2 frames before it | Not checked: it needs the picture |
| Where to break a line | After punctuation, before conjunctions and prepositions; a longer bottom line is preferred | At logical points, ideally at punctuation | At a logical, grammatical break | Not checked: it needs a reader |
A dash means we found no figure for that rule in that guide. Sources checked on 9 November 2026: the Netflix English (USA) style guide updated 19 December 2025, Netflix timing guidelines updated 4 July 2025, BBC Subtitle Guidelines version 1.2.5 (March 2026) and the Prime Video Subtitling Guidelines of 1 May 2026. The check uses the Netflix adult limits; it does not switch to BBC or Prime Video numbers.
Sources: Netflix English (USA) Timed Text Style Guide · Netflix General Requirements · Netflix Subtitle Timing Guidelines · BBC Subtitle Guidelines · Prime Video Subtitling Guidelines
Which Subtitle Guidelines to Follow
There is no single standard. Follow the guide of whoever receives the file; if nobody sets one, the Netflix numbers are a common default.
Platforms
Delivering to a streaming service
Follow its own guide to the letter, including the guide for each language. Prime Video’s reading speed of 17 characters per second is stricter than Netflix’s 20, so a file that passes one platform can fail the other.
Captions
US captions for education and TV
The DCMP Captioning Key, used for educational media, sets reading speed in words per minute: up to 130, 140 or 160 depending on the level of the audience, with each caption shown for at least 40 frames and at most 6 seconds. FCC rules for TV ask for accurate, synchronous, complete and well-placed captions, but set no character counts.
Your own videos
YouTube, courses and social video
No platform checks your numbers, so readability is the only test. Two lines of up to 42 characters at 20 characters per second is a safe default; for vertical video, keep lines shorter, since the frame is narrow.
How to Check Subtitles Against the Guidelines
Three steps, all in your browser.
Open your file
Drop an SRT, VTT or SBV file on the editor. The Check window opens with a count of errors, warnings and readability tips.
Go through the tips
Readability tips are lines over the limits: too many rows, a row over 42 characters, more than 20 characters per second, under 0.83 or over 7 seconds. Click one to jump to its line.
Fix and export
Shorten the text, split a long subtitle or give it more time, and the count updates as you edit. Then export SRT or VTT.
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