Subtitle standards explained: Netflix rules, reading speed and French norms
Characters per line, reading speed in CPS, duration and line breaks. The Netflix numbers, the tighter French tradition, and the one rule that gets files rejected.
By Hanna Eng·Video editor, Free Conservatory of French Cinema
On Netflix, a subtitle is at most 42 characters per line, 2 lines maximum, held for 5/6 of a second to 7 seconds, at a reading speed of 17 characters per second for adult programmes (13 for children's). Traditional French subtitling is tighter: roughly 36 to 42 characters per line and about 14 to 15 characters per second.
Good subtitles are invisible: the viewer reads them without noticing they are reading. That comfort is not an accident, it comes from a small set of measurable rules about how much text fits on screen and how long it stays there. Netflix publishes the strictest, most-cited version of those rules, and traditional French subtitling is tighter still. Here is what the numbers are and why they matter.
Subtitle limits: Netflix vs traditional French practice
| Parameter | Netflix (France) | French tradition |
|---|---|---|
| Characters per line | 42 | ~36 to 42 |
| Lines | 2 maximum | 2 maximum |
| Reading speed, adult | 17 CPS | ~14 to 15 CPS |
| Reading speed, children | 13 CPS | lower |
| Minimum duration | 5/6 s (0.833 s) | 16 frames (~0.67 s) |
| Maximum duration | 7 s | 5 s |
| Gap between subtitles | 2 frames minimum | 4 frames minimum |
Netflix Timed Text Style Guide; traditional French subtitling practice (CST / historical laboratory norms; ATAA professional guidance). The French-tradition figures are conventional ranges, not a single sourced spec.
What the rules actually control
Every subtitle standard controls four things: how many characters fit on a line, how many lines show at once, how long each subtitle stays on screen, and how fast the text scrolls past, measured in characters per second (CPS). Get these right and the viewer keeps up effortlessly. Get them wrong and the subtitle is either unreadable or distracting.
The numbers differ by platform and country, but the logic is universal: a subtitle has to be short enough to read in the time it is visible, and timed so the eye is not fighting the picture.
Netflix subtitle rules in numbers
Netflix's Timed Text Style Guide is the reference most clients mean when they say broadcast quality. For French, a line is capped at 42 characters, with a maximum of 2 lines on screen. Each subtitle stays up for at least 5/6 of a second (0.833 s) and at most 7 seconds, with a minimum 2-frame gap between consecutive subtitles.
Reading speed in the French (France) Timed Text Style Guide is capped at 17 characters per second for adult programmes and 13 for children's content; this is the per-language French value, not a single Netflix-wide CPS number. The English guide is slightly looser on speed (20 CPS adult), which is why the same translation can pass in one language and fail in another. The table above lays out the full set.
French subtitling norms are tighter
Traditional French subtitling, the practice codified by the ATAA and used in cinema and broadcast, is more conservative than Netflix. Lines usually run about 36 to 42 characters, and the comfortable reading speed is closer to 14 to 15 characters per second.
The reason is editorial, not technical: French subtitling has a long tradition of condensing dialogue rather than transcribing it, so the viewer reads less and watches more. Knowing which standard a project follows, the platform spec or the French tradition, is the first question to settle before a single line is written.
Norms by delivery: cinema, TV and social
The measurable rules shift with where the subtitle plays. Cinema and festival subtitling holds the tightest tradition: two lines maximum, conservative reading speeds, and timing cut to the rhythm of the scene. Broadcast television adds its own layer, often delivered as EBU-STL with channel-specific reading-speed and line-length limits, and increasingly a separate SDH track for accessibility.
Social and web video is the loosest on format but the harshest on attention. Subtitles are usually burned in, because most feeds autoplay muted and viewers never toggle a track, and they run faster and shorter than a cinema subtitle because the viewer is scrolling. Vertical formats squeeze line length further. The reading-speed discipline still matters, but the house style is shorter phrases, higher contrast, and captions designed to be read on a phone in a noisy room.
Reading speed (CPS) is the rule people fail
Character-per-line limits are easy to see; reading speed is the one that quietly fails a delivery. CPS is the visible character count divided by the time the subtitle is on screen. A line that fits on 42 characters can still be rejected if it flashes by in a second, because that is well over 17 CPS.
Spaces and punctuation count toward the total. The fix is almost always to condense the text or extend the subtitle's duration, not to cram more characters in. Reading speed above the cap is one of the most common readability reasons a file gets sent back, alongside technical issues like wrong framerate, illegal gaps or format errors.
Line breaks and duration that read well
Where you break a line matters as much as its length. Break at a natural grammatical point, after a clause or a piece of punctuation, never mid-word or in a way that splits a noun from its article. Keep to 2 lines, and prefer a slightly longer single line over an awkward two-line split.
Timing follows the same comfort logic. On Netflix, a subtitle is never shorter than 5/6 of a second (0.833 s) and never longer than 7; traditional French and cinema practice uses a shorter maximum (the table's 5 s), so the upper limit is platform-dependent, not universal. Always leave a small gap between events so consecutive subtitles do not appear to merge.
SME and SDH captions are a different job
Standard subtitles assume the viewer can hear. Captions for deaf and hard-of-hearing audiences add speaker identification and non-speech sounds such as music and effects. France uses the SME standard (sous-titrage pour sourds et malentendants), which is colour-coded to mark who is speaking; the English-language equivalent, SDH, serves the same accessibility purpose but follows its own, usually monochrome, conventions.
Under French law and the Arcom accessibility framework, the SME obligation depends on a channel's audience share: large channels above the legal threshold must subtitle close to 100% of their programmes, while smaller channels have a reduced or no obligation. If a brief mentions accessibility, the deliverable is SME, not plain subtitles, and the rules above are applied on top of the captioning conventions.
Common subtitling mistakes
The recurring errors are all readability failures: lines over the character limit, reading speed above the cap, three lines on screen, no gap between events, and breaks that split a phrase awkwardly. Each one makes the viewer work, which is exactly what good subtitling avoids.
In DaVinci Resolve you can build and time subtitles on a dedicated subtitle track, and Resolve does flag reading speed for you: set a maximum characters-per-second threshold in the subtitle settings and the CPS value turns red whenever a subtitle exceeds it. You still decide how to fix it, by condensing the line or extending its duration.
Frequently asked questions
How many characters per line should a subtitle have?
Netflix allows up to 42 characters per line; traditional French subtitling stays around 36 to 42. Both cap subtitles at 2 lines, and spaces count toward the total.
What reading speed should subtitles use?
Netflix caps reading speed at 17 characters per second for adult programmes and 13 for children's. Traditional French practice is tighter, about 14 to 15 CPS.
What are Netflix's subtitle rules?
For French: 42 characters per line, 2 lines maximum, 17 CPS for adults (13 for children), a minimum duration of 5/6 of a second, a maximum of 7 seconds, and at least a 2-frame gap between subtitles.
How long should a subtitle stay on screen?
On Netflix, between 5/6 of a second (0.833 s) and 7 seconds, long enough to read at the target reading speed but not so long it lingers after the line has been read. Traditional French and cinema practice uses a shorter maximum (around 5 s), so the upper limit depends on the platform rather than being universal.
Do spaces count in the subtitle character limit?
Yes. Spaces and punctuation count toward both the per-line character limit and the reading-speed calculation.
What is the difference between subtitles and SME captions?
Subtitles assume the viewer can hear. SME, France's colour-coded accessibility standard (the English-language equivalent is SDH), adds speaker identification and non-speech sounds for deaf and hard-of-hearing viewers. Under the Arcom framework the obligation depends on audience share: large channels must subtitle close to 100% of programmes, while smaller channels have a reduced or no obligation.
Why was my subtitle file rejected?
A frequent cause is reading speed above the limit: the text is correct but on screen too briefly. Condense the line or extend its duration rather than adding characters. Technical failures (wrong framerate, illegal gaps, format or metadata errors) are at least as common in automated QC.