Subtitle rules: line length, reading speed, and timing

Why do subtitles have rules at all?

Someone watching a subtitled video is reading text, watching the picture, and listening to the audio at the same time. Every second they spend reading is a second they are not looking at the screen. Subtitle rules keep the reading easy so the text helps the video instead of getting in its way.

Professional subtitlers and broadcasters worked out these practical conventions, and clients and platforms later wrote them into their style guides. Think of them as working standards rather than strict laws. The exact numbers shift a bit from one guide to the next, but the underlying principles stay the same.

How long can a subtitle line be?

Forty to forty-two characters per line, counting spaces and punctuation, across at most two lines, is a common ceiling. Some style guides ask for fewer characters on smaller screens. Shorter lines need less eye movement and sit neatly under the action.

Put short sentences on a single line. When a sentence is longer, break it across two lines of roughly equal length, or keep the top line shorter so the text covers less of the image. If you need a third line, you should almost always split the subtitle into two separate cues instead.

How fast can viewers read subtitles?

Reading speed is measured in characters per second, which is just the character count divided by how long the subtitle stays up. Most professional guides put the adult limit between fifteen and twenty characters per second. Aim lower for children, technical or dense speech, and people reading in a second language.

When someone speaks faster than the reading limit, you cannot include every word. Instead, condense the text. Cut filler words, false starts, and repetitions. Preserve the core meaning and tone, and let the visuals and audio carry the rest of the context.

A quick calculation shows why. At seventeen characters per second, a two-line subtitle of sixty-eight characters needs about four seconds on screen. If the speaker says it in two and a half seconds, you can either cut the text down to around forty-two characters or hold the subtitle a bit longer if the next line of dialogue leaves room. Run those numbers any time a subtitle feels rushed.

How long should a subtitle stay on screen, and when should it appear?

Even a one-word subtitle needs time to register, so one second is the usual minimum. At the other end, a subtitle that sits on screen for more than six or seven seconds starts to feel stuck and should be shortened or split. Leaving a gap of a few video frames between one subtitle and the next also helps the eye notice that the text has changed.

Bring a subtitle in right as the speaker starts talking and take it off shortly after they stop. When a camera cut falls close to a subtitle change, line the timing up with the cut. Treat timestamps from an automated transcript as a starting point, and expect to nudge start and end times by fractions of a second.

Where should you break a line?

Break a line where the meaning breaks, not simply where the character count runs out. Keep words that belong together on the same line: an article with its noun, an adjective with its noun, a preposition with its object, a person's first and last name, an auxiliary verb with its main verb. When you have a choice, break right after punctuation or just before a conjunction.

Read every two-line subtitle back to check how the split lands. If the first line makes sense as a unit and the second line picks up naturally, the break is in the right place. If you stumble reading it out loud, move the break.

Do the rules change for Hebrew and Arabic?

The principles stay the same, but the script changes what a character count means. Hebrew is usually written without vowels and glues short prefixes onto the front of words, so forty characters pack in more words in Hebrew than in English. Arabic letters change shape depending on where they sit in a word. In both languages, dropping in English words or digits can throw punctuation out of order, so check every mixed-script line with your own eyes.

When a client gives you no limits for Hebrew or Arabic, check the target platform's language guidelines and ask for an approved sample file. KolWrite lets you edit the text before you export to SRT or VTT, or before you burn captions straight into the video. Always check your work during video playback, since only the player shows how the lines actually render.