There is no single number
Ask how many characters fit on a subtitle line and you will get different answers depending on who you ask. Many guides for television and streaming land somewhere in the high thirties to low forties for Latin-alphabet languages, while others allow more or fewer. Some guides for other scripts set quite different figures. Treat any single number as one guide’s choice, not a universal fact.
What stays constant is the reason a limit exists: a line has to fit comfortably on the screen, in a size people can read, without spreading so wide that the eye has to travel far from the action.
What shapes the limit
Screen width and safe margins
Text has to sit inside the visible picture with a margin on each side, since some displays crop edges. The width left over is the space available. A wide screen allows a longer line than a narrow one, but only up to the point where readability falls, which is why the picture’s width is not the only factor.
Font and size
Larger text means fewer characters across the same width. Proportional fonts also vary: a line of narrow letters fits more than a line of wide ones, so a count of characters is always an approximation. Guides often count every character, including spaces and punctuation, because it is simple to check automatically. The effect of font and size is discussed in the piece on font, size and contrast.
How the eye reads
Eyes read in short jumps. Very long lines force bigger movements and make it harder to find the next line. Lines that are too short break the thought into too many fragments. A moderate line, which can be taken in with a quick sweep, is the compromise. The viewer also has to look back to the picture, so every extra character costs a little attention.
Reading time
A longer line takes longer to read, and the time available is set by the cue’s duration. Line length therefore connects to reading speed and display duration. If speech is quick, packing the maximum onto each line can push the speed past what viewers can follow. Many writers would rather shorten the text than stretch the limits.
Language and script
Languages differ in how much text a given meaning needs. Translations from English into some languages tend to run longer, a problem covered under text expansion. Some others can run shorter. The same limit therefore feels tight in one language and roomy in another.
Scripts matter too. Languages written without spaces between words need different handling, as covered in the article on word segmentation, and logographic scripts such as Chinese characters carry more meaning per character, so guides typically set a much lower character count per line for them. Right-to-left scripts follow the same limits idea but add display rules of their own; see right-to-left scripts. Because of all this, guides set limits per language rather than applying one number everywhere.
Counting is only a rough check
A hypothetical illustration: suppose a guide allows 42 characters per line and two lines per subtitle. That would allow up to 84 characters in a cue (42 times 2). The sentence “I told you we would be late if we stopped” has 41 characters including spaces and fits on one line. A longer sentence of 60 characters needs two lines, and the writer must choose where to break it. The count is useful, but a line that meets the limit can still read badly if it breaks in an awkward place, as explained in the article on line breaks.
Counting also ignores width. A line of 40 narrow letters and a line of 40 wide capitals can occupy very different widths. Tools that measure actual rendered width are more precise than character counts, though counts remain popular because they are easy to apply and check.
Balance between lines
When a subtitle has two lines, they do not have to be equal. Some guides like a pyramid shape, with a shorter top line and longer bottom, because the top line then covers less of the picture. Others prefer an inverted shape or equal lengths. The choice depends on grammar as much as shape, and the grammar should usually win. The two-line convention itself has its own explanation under the two-line limit.
Why not just use smaller text?
It is tempting to shrink text to fit more per line, but this defeats the purpose. Small text is harder to read, especially for older viewers and for anyone watching on a small screen or from a distance. Making text smaller trades one problem for a worse one. It is generally better to cut or rephrase, which is the craft of text condensation, than to shrink.
When limits are bent
Occasionally a line goes slightly over, for example to avoid a bad break or to keep a name intact. Guides often allow this within reason, though overshoot should be rare and stay within the screen’s safe area. On the other hand, some situations call for a stricter limit than normal, such as content for children subtitles, small screens or loud environments.
Practical advice
- Use the limit your client or platform specifies; where there is none, pick a reasonable one and apply it consistently.
- Check the limit against the real font and the smallest screen the audience uses.
- Treat the count as a guide and let readability make the final call.
- Check line length as part of a regular quality checklist, since it is easy to measure automatically.
A limit is not a goal. A short, clear line that sits comfortably inside it is better than one that squeezes in as many characters as possible.