Subtitle Readability: Line Length, Timing and Placement That Work on a Phone
Good subtitles disappear: the viewer reads them without noticing. Bad ones are too long, too fast, or sit under a button. These widely used guidelines come from broadcast and streaming subtitling and adapt well to vertical short-form video.
The core numbers
| Rule | Typical guideline | Why |
|---|---|---|
| Characters per line | About 42 or fewer | Longer lines force small text or tiny margins on a phone. |
| Lines on screen | Two at most | Three lines cover the picture and take too long to read. |
| Reading speed | Around 17 characters per second for adult audiences; slower for children | Faster text cannot be read comfortably while watching the video. |
| Minimum on-screen time | Roughly 1 second per cue | Shorter cues flash by. |
| Maximum on-screen time | About 6-7 seconds per cue | Longer cues feel stuck and viewers read ahead. |
These are guidelines, not laws. Short-form video often runs a little faster than a film, and a punchy hook can sit on screen for just a moment. If viewers have to re-watch to finish a line, it is too fast.
Break lines at natural pauses
Split a caption where you would pause when speaking. Avoid separating tightly linked words, such as an article from its noun, a preposition from its object or a name across two lines. Lafzaly follows the same idea when it builds captions: it starts a new line at a pause in the speech, after punctuation, or when a line reaches about 9 words or 42 characters.
Awkward: Canal Road par bohat
achi location mein plot
Better: Canal Road par
bohat achi location mein plot
Sync captions to the voice
A caption should appear when the speaker begins the phrase, or a fraction of a second before, and disappear soon after they finish. Word-level timestamps make this much more accurate than one long block per sentence, because each short line can follow the actual rhythm of speech.
Make them readable
- Contrast. White text with a dark outline or a semi-transparent box stays readable over bright and busy footage.
- Size. If you cannot read it at arm's length on your phone, it is too small.
- Font. Choose one clean, bold sans-serif and use it everywhere in the video.
- Emphasis. Highlight one key word per caption at most. If everything is highlighted, nothing stands out.
- Consistency. Keep the same position, font and colours from the first second to the last.
Placement
Keep captions inside the safe zone: away from the very bottom edge and the right side, where the platform shows its buttons and your description. Do not cover the speaker's mouth or on-screen text. If a lower-third graphic appears, move the captions for that moment.
Write for the eye, not just the ear
- Edit for brevity. It is fine to shorten spoken fillers when exact verbatim text is not required.
- Spell numbers and names consistently.
- Put a question mark on every question.
- For Roman Urdu, use one spelling per word. See the Roman Urdu writing guide.
A final pass
- Play the video once with sound off, reading only the captions. Does the message still make sense?
- Play it again at normal speed. Do any lines feel rushed?
- Watch it on a phone, inside the actual app, to check the safe zones.
Adjust timing line by line
In Lafzaly you can edit the text and the start and end time of every subtitle line, then preview it with caption presets before exporting.
Open Lafzaly