A subtitle file can be right word for word and still be tiring to watch. One line runs almost from edge to edge, the next blinks off before anyone finishes reading it, and somewhere a “the” hangs at the end of the top line while its noun waits underneath.
Viewers rarely name any of this. They just say the subtitles were hard to follow.
Most of what makes subtitles readable comes down to a short list of numbers. Knowing why each one exists makes it easier to decide when you can bend it.
The reference most people reach for is Netflix’s Timed Text Style Guide, because it’s public and published per language. Broadcasters and other platforms have their own. When a client’s delivery spec names a guide, that guide wins.
In short
- The common benchmark is 42 characters per line and two lines at most, and a client’s delivery spec overrides it.
- Netflix’s English guide allows up to 20 characters per second for adult programs and its Brazilian Portuguese guide 17, so faster speech means cutting words.
- Each subtitle stays up between five sixths of a second and 7 seconds, with at least 2 frames before the next one.
- In and out points move to a cut that falls within half a second.
- Break lines by meaning, and use shorter lines for vertical video, which has no single standard.
| Rule | Common benchmark | What it protects |
|---|---|---|
| Characters per line | 42, spaces and punctuation included | The picture, and how far the eye travels |
| Lines per subtitle | 2 at most | The picture |
| Reading speed | 17 to 20 characters per second for adults | Time to read and still watch |
| Minimum time on screen | 5/6 of a second (20 frames at 24 fps) | Subtitles that flash |
| Maximum time on screen | 7 seconds | Subtitles that get read twice |
| Gap between subtitles | 2 frames | Seeing that the text changed |
| Shot changes | In and out points move to a cut within half a second | Subtitles that straddle the edit |
Characters per line, and why only two lines
Netflix’s English (USA) and Brazilian Portuguese guides both cap a line at 42 characters, and you count everything, spaces and commas included. A longer line needs a smaller font or runs closer to the edges of the frame. Either way the eyes spend longer away from the faces on screen.
The two-line limit comes from the same place. A third line covers a big piece of the lower frame, which is often where the lower third or the product sits.
The guides also ask you to keep a subtitle on one line unless it doesn’t fit. When it has to go to two, Netflix prefers what it calls a bottom-heavy pyramid, with the lower line the longer of the two. A long line over a two-word stub is harder to take in at a glance.
Reading speed in characters per second
Reading speed is measured in characters per second (CPS): the characters in the subtitle, spaces included, divided by the seconds it stays on screen. The limit depends on language and audience.
Netflix’s English (USA) guide allows up to 20 CPS for adult programs and 17 for children’s programs. Its Brazilian Portuguese guide is stricter, with 17 for adults and 13 for children.
A full two-line subtitle of 70 characters needs a little over 4 seconds at 17 CPS, and 3.5 seconds at 20. If the speaker gets through that sentence in two seconds, the subtitle has to lose words.
Filler words and repetition go first. After that, anything the picture already shows.
How long a subtitle stays on screen
Netflix sets the minimum at five sixths of a second, which is 20 frames at 24 fps. Anything shorter reads as a flash, even a single word. The maximum is 7 seconds, because a subtitle that sits there longer tends to get read a second time.
At the end of a sentence, the subtitle should stay up for about half a second after the person stops talking, as Netflix’s timing guidelines recommend. Cutting it on the last syllable feels abrupt.
Between two subtitles there should be at least 2 frames. Without that gap, consecutive subtitles look like one block of text changing in place, and the eye can miss that a new line arrived.
Netflix also asks you to close short gaps. At 24 fps, anything from 3 to 11 frames gets pulled in to 2, so the text doesn’t blink off and back on for a third of a second.
Shot changes
Netflix’s timing guidelines use half a second around a cut as a window. If someone starts talking on the cut or within half a second after it, the subtitle comes in on the first frame of the new shot.
If a subtitle would go out within half a second of a cut, it ends two frames before the cut instead. The guide says this is so subtitles “fit neatly within the edit of the content.”
A subtitle that hangs over a cut by a few frames looks like a mistake, and viewers often read it again because the new shot feels like a new moment.
Here the editor has an advantage over a subtitler working from an exported file, because you know where every cut is.
Breaking lines by meaning
Where you break a line matters as much as how long it is. Netflix’s guides say to break after punctuation and before conjunctions and prepositions. They also list what should stay together on one line:
- an article and its noun
- an adjective and its noun
- a first and last name
- a subject pronoun and its verb
- a verb and the preposition it takes
- an auxiliary, reflexive pronoun or negation and the verb it goes with
Here are two ways to split the same subtitle:
Three days, two thousand people and one
plan for the year ahead.
Three days, two thousand people
and one plan for the year ahead.
The first one stops on “one” and makes the reader wait for the noun. The second breaks before “and”, where anyone reading the sentence aloud would pause anyway, and the lines come out at 31 and 32 characters.
The same thinking applies when a sentence runs across two subtitles. Change subtitles where a clause ends, and keep names, numbers and their units in one piece.
Vertical video
Vertical has no equivalent of the 42. A 2019 Nimdzi article on subtitling vertical video noted there was no standard for characters per line in that format and suggested staying at or under 37, depending on font size.
The frame is narrower and the platform’s buttons and captions cover the bottom and the right side, so lines get shorter and subtitles usually sit higher than on a 16:9 master.
Whatever number you choose, check it on a phone and add it to your final QC checklist.
How this works in RecReview
In RecReview you transcribe a video in Portuguese, English or Spanish, or let it detect the language from the speech. Subtitles come from that transcript and show up in the review player with the CC button, or Shift+C.
They’re built to the limits above. Lines go up to 42 characters, two lines at most, with a target of 17 characters per second.
Each subtitle stays on screen between five sixths of a second and 7 seconds, holds for half a second after the speech ends, and keeps 2 frames from the next one, with gaps under half a second closed.
When RecReview has the video’s cut points, it moves the in and out points onto a cut that falls within half a second.
A subtitle of up to 30 characters stays on one line, and a longer one goes to two lines of similar length when there’s a good place to break. The engine avoids leaving a single word alone on a line.
An AI reads each sentence and marks where it can break, between groups of words that belong together. A rules engine then builds the subtitles only at those marks, counting characters and time.
Where the AI leaves a stretch unmarked, rules for Portuguese and English steer a line away from ending on an article, a preposition, an auxiliary verb or a negation.
Workspace owners, admins and editors can click a subtitle in the player and fix the text right there, with a counter on each line against the 42-character limit. The timings stay as they were built.
Once you edit subtitles by hand, that version is the official one, and RecReview won’t rebuild it if the transcript changes later.
SRT and VTT exports carry the same subtitles you see in the player, edits included, and the transcript also exports as TXT or JSON. When the cut is ready to go out, here’s how to send it to the client for review.
