Subtitle Readability: Line Length, Reading Speed and Line Breaks

Translation craft · 5 min read · Updated 21 October 2026

The rules that make subtitles easy to read: characters per line, reading speed (CPS), minimum and maximum durations, and where to break lines.

A subtitle is only good if people can read it in the time it's on screen, while also watching the picture. Accurate translations fail this test all the time: the line is correct, but it's too long, it flashes past too quickly, or it's broken in a place that makes the viewer re-read it. This guide covers the readability rules professional subtitlers use, and how to apply them when you translate.

Why readability is harder in translation

Languages don't take the same space to say the same thing. Translating from English into many European languages adds length; translating into Hindi or Hinglish can add or remove words depending on register; Japanese and Chinese source lines are short in characters but dense in meaning. A translation that's faithful word for word can easily run 30-40% longer than the original - and the timing doesn't get longer with it.

So readability is not a final polish step. It's part of translating.

Rule 1: keep lines short

Characters per line (CPL) is the most common limit. Widely used professional guidelines - including Netflix's timed text style guides for many languages - set a maximum of about 42 characters per line for Latin-script languages. Broadcasters often use slightly shorter limits, around 37 characters.

Why it matters: the eye takes in a short line in one or two fixations. A long line forces the viewer to scan across the screen and away from faces and action.

In practice:

• Aim for 42 characters or fewer per line.
• Use at most two lines per subtitle.
• Prefer one line when the text fits comfortably.

Rule 2: respect reading speed

Characters per second (CPS) measures how fast viewers have to read: the number of characters in a subtitle divided by how long it's on screen.

Common professional targets for adult content are up to around 17-20 characters per second, with lower limits for children's programming. A two-line subtitle of 80 characters therefore needs about four seconds on screen to be comfortable.

When the CPS is too high, you can't make the dialogue slower, so you make the text shorter:

• remove filler ("well", "you know", "I mean") that doesn't change the meaning;
• drop repetition the audio already conveys ("No, no, no!" → "No!");
• use shorter synonyms;
• simplify sentence structure.

This is called condensing, and it's a core subtitling skill. A good subtitle carries the meaning and tone, not every word.

Rule 3: durations that the eye can follow

Two duration limits keep subtitles readable:

• Minimum duration. Very short flashes are hard to read even if the text is short. Many guidelines use a minimum of roughly five-sixths of a second (about 0.83 s) for any subtitle.
• Maximum duration. Subtitles that sit on screen too long get re-read, which is distracting. A common maximum is about seven seconds; longer speech is split into several subtitles.

Leave a small gap between consecutive subtitles - a couple of frames - so the viewer's eye registers that the text has changed.

Rule 4: break lines in the right place

When a subtitle needs two lines, where you break matters more than most people think. A good break follows the grammar of the sentence, so each line is a meaningful chunk.

Break after:

• punctuation (commas, full stops, question marks);
• complete clauses.

Break before:

• conjunctions ("and", "but", "because");
• prepositions that start a phrase ("to the station", "in the morning").

Never separate:

• an article from its noun ("the / car");
• a first name from a surname;
• a verb from its auxiliary ("will / go") where you can avoid it;
• a number from its unit.

Many style guides also prefer a bottom-heavy shape - a shorter top line and a longer bottom line - because it keeps more of the picture visible, though a good grammatical break matters more than the shape.

Example

Bad: "I can't believe you went to the / station without telling me."

Better: "I can't believe you went to the station / without telling me."

Rule 5: two speakers, one subtitle

When two people speak within one subtitle, put each speaker on their own line, usually starting each line with a hyphen:

- Are you coming? - Not tonight.

Some style guides use a hyphen only on the second line; pick one convention and use it throughout.

Rule 6: italics, capitals and punctuation

• Italics usually mark voices that aren't physically present in the scene: off-screen narrators, voices on a phone, thoughts, song lyrics.
• All capitals are hard to read and usually reserved for on-screen text that's in capitals.
• Ellipses show trailing off or an interruption; don't overuse them.
• Keep punctuation consistent with the target language's conventions.

Applying this when you translate with AI

AI models don't count characters reliably on their own, and they tend to translate faithfully rather than concisely. Two things help:

1. Say it in the instructions. Ask for short, natural lines suited to subtitles, and for condensing when the meaning allows. SubFly's style presets and custom prompts include this kind of instruction so it applies to every batch.
2. Review with readability in mind. Watch the episode at normal speed. Any subtitle you can't finish reading before it disappears needs condensing. Fix the worst ones; they're usually a small fraction of the file.

Keep the translated file's timing exactly as the source's - change the words to fit the time, not the time to fit the words. That keeps the translation in sync and makes it easy to compare with the original.

Quick reference

These are conventions, not laws - different platforms and languages adjust them - but following them will make your translated subtitles feel professional. For the bigger picture of a translation project, read the complete guide to translating anime subtitles, and for keeping a consistent voice, see the fansub style guide.