Subtitle reading speed and line length, explained

The short answer

Most professional guidelines keep subtitles at or below about 20 characters per second for adult viewers, with at most two lines of around 42 characters each, and each caption on screen for roughly one to seven seconds. Children's programs and less experienced readers need slower subtitles.

These are guidelines, not laws of nature. Different broadcasters and platforms set different numbers, and they all say that well-edited text matters more than hitting an exact figure. Still, a file that breaks the usual limits again and again is hard to watch, and some platforms reject files that do.

What characters per second means

Characters per second, often written CPS, is the number of characters in a caption divided by the time it stays on screen. A caption of 40 characters shown for two seconds runs at 20 characters per second. Letters, spaces and punctuation all count, because the eye still has to travel over them. Line breaks and formatting tags are not counted.

Some guidelines use words per minute instead. Words vary in length, so characters per second is the more precise measure for checking a file, but both lead to similar results for English.

00:00:09,400 --> 00:00:12,500
We have about ten minutes
before the lights go out.

Characters: 25 + 25 = 50 (the line break is not counted)
Time on screen: 12.5 s - 9.4 s = 3.1 s
Reading speed: 50 / 3.1 = about 16.1 characters per second

What published style guides recommend

The figures below come from two widely cited guides as they read in October 2026. Netflix publishes separate guides for each language, with different limits for many of them; the English (USA) guide is shown here. The BBC guidelines cover broadcast and online video.

Why line length and line count matter

Long lines make the eye travel further from the picture and can run off the edge on small screens or in large fonts. Two lines are the usual maximum because a third covers too much of the picture. When a caption is too long, it is better to split it into two captions shown one after the other than to squeeze it onto three lines.

Where you break a two-line caption also matters. Guidelines generally prefer breaks at natural pauses, such as after punctuation or before a conjunction, rather than in the middle of a phrase.

Why time on screen has limits

A caption that flashes by in half a second is gone before most people have read it, even if it has only a few words. That is why guidelines set a minimum time on screen. A caption that stays for ten seconds is a problem too: viewers read it, look back at the picture, then start reading it again. Long silences are better shown with no caption at all.

Overlaps are a separate problem. When a caption is still on screen as the next one starts, many players show both at once, stacked, which looks like a mistake and is hard to follow.

Check your own file

The subtitle checker on this site reads your file in the browser and lists every caption that breaks a rule, with its number and start time. Its starting values are 20 characters per second, 42 characters per line, two lines per caption, at least one second and at most seven seconds on screen. It also flags every overlap. You can change any value, for example to 17 characters per second for a children's program or 37 characters per line for broadcast, and the list updates at once.

Above the list, the checker shows how many captions have problems, the average and highest characters per second, and the longest line. You can download the list as a text report. The checker's shortest time is one second, slightly stricter than the five sixths of a second in the Netflix guide; lower it to 0.8 if you work to that guide.

A good routine is to check the file once with the default values to see the overall picture, then set the limits your platform or client asks for and work through the list from the top. Fix the captions with the highest reading speed first; they are the ones viewers are most likely to miss.

How to fix captions that are too fast

The checker reports problems; it does not rewrite your captions. Fix them in a text editor or a subtitle editor, then check the file again.

• Let the caption stay longer, if there is a gap before the next one.
• Shorten the text by removing repetitions, filler words and false starts that do not change the meaning.
• Split a long caption into two shorter ones, each with its own part of the time.
• Join two very short captions that belong together into one.
• Remove sound descriptions or speaker names that the audience does not need, with the subtitle cleaner, when the file is not meant for viewers who are deaf or hard of hearing.

Reading speed in other languages

The figures above are for English. Languages with longer words, different scripts or different reading habits often use other limits. Netflix, for example, publishes a separate style guide for each language it works with, and the numbers in them are not all the same. If you subtitle in another language, look up the guide for that language and enter its limits in the checker.

The checker counts every character the same way, whatever the script. It does not know about the language of the file, so the limits you enter are the only thing that decides what counts as too fast.

A note on automatic captions

Captions created by speech recognition often break many rules at once: very short captions, lines that repeat as words are added, and overlapping timings. Running the subtitle cleaner first to join repeated captions and end overlaps, then the checker, usually leaves a much shorter list of real problems.

Common questions

Is 20 characters per second always too fast? No. It is a common upper limit for adult viewers, not a target. A whole file running close to it is tiring to watch; a few short exclamations above it are usually fine.

Where does 42 characters per line come from? It is the limit in many streaming guidelines, including the Netflix English guide. Broadcast teletext subtitles have long used 37, which is why the BBC still applies that number to broadcast.

Do spaces count? Yes, in the checker and in most guidelines, because viewers read past them. Line breaks and formatting tags do not count.

Does the checker change my file? No. It only reads the file and creates a report. Your subtitles are not changed or uploaded.