Reading speed: the limit a subtitle cannot argue with
Reading speed is how much text a viewer can take in per second. Distributors publish limits for it, the limits differ by language and by audience age, and in a vertical frame the line width usually runs out before the reading limit does. As of 2026-09-22.
| Limit | Set by | Binds first in a vertical frame |
|---|---|---|
| Characters per second | Distributor guidelines, by language and audience | Usually not |
| Characters per line | The width of the safe area | Usually yes |
| Lines per subtitle | Composition, not readability | Two is the working maximum |
| Minimum duration | Distributor guidelines | Rarely |
Inclusion rule. The published limits that constrain a subtitle. All are set outside the tool, by platforms and by the shape of the frame. Order. Fixed order, the readability limit first.
1The limit is published, and it is not a preference
Characters per line and characters per second appear in distributor specifications, and the figures for younger audiences are meaningfully lower. A subtitle that fits the frame can still exceed the reading limit.
So a translation has to be cut rather than compressed. That is a translation decision taken under a constraint the translator did not set, and it is why subtitles are shorter than the dialogue they carry.
2A narrow frame changes which limit matters
In a vertical frame the safe area for text is narrow, so two lines is the working maximum and three is a different layout rather than a compromise: it covers the part of the picture the shot was built around.
Cutting the sentence is cheaper than moving the subtitle. That is the practical ordering, and it means the frame shape constrains the language work in short vertical video more than the reading limit does.
3Nothing about it appears in a language list
No vendor read for this register publishes reading-speed handling, line limits or what it does when a translated line will not fit. A language count cannot express any of it.
It is recorded here as a term rather than as a column, because a column with no vendor entries would be a question pretending to be a measurement. The constraint is real whether or not anybody documents it.
A definition, not a measurement: no vendor figure appears here that is not also in the register. The register keeps subtitle constraints out of the voice column entirely.
Nearby terms: Text inside the frame, Text expansion. The whole vocabulary is at terms; nothing on this page is a claim about a named product.