Subtitle Timing and Reading Speed: Practical Guidelines

The core numbers

Major streaming services publish style guides with similar limits for English subtitles, and most professional subtitlers follow them. As a working summary:

Different platforms and languages adjust these figures, so always read the guide of the platform you are delivering to. Broadcast guidelines in the UK are often expressed in words per minute (roughly 160–180 words per minute for pre-recorded programmes).

Characters per second (CPS)

CPS is the number of visible characters in a subtitle divided by the time it is on screen. A 40-character line shown for 2 seconds runs at 20 CPS, which is the upper limit for adults. Fast speakers often exceed that, so subtitlers condense the text: they remove fillers, repetitions and obvious words, while keeping the meaning. You can measure your own file with the reading speed analyser.

Line length and line breaks

Lines above about 42 characters are hard to read on TV and force a small font on mobile. Break lines at natural points: after punctuation, before conjunctions and prepositions, and never in the middle of a name, number or verb phrase. Prefer a bottom-heavy pyramid shape (shorter top line) for two-line subtitles.

Minimum and maximum duration

A subtitle shown for less than about 0.8 seconds appears as a flash and is hard to read even if it has two or three words. If speech is brief, extend the end time into the silence that follows. On the other hand, a subtitle that stays for more than 7 seconds feels disconnected from the speech; split long statements into several cues.

Syncing to speech

• Start the subtitle at the moment the speaker begins, or up to a few frames earlier.
• End it as the speech ends; leave a short tail (up to about half a second) if no new subtitle follows.
• Align changes with shot cuts where possible, so the subtitle does not straddle a cut.

How to apply the rules

1. Run the file through the SRT checker to list overlapping and out-of-order cues.
2. Open the reading speed analyser and fix the cues flagged as fast by shortening the text or extending the time.
3. Review cues over 42 characters per line and re-break them.
4. If you create subtitles from a script, the TXT to SRT tool helps you start with sensible durations.

Languages that need special treatment

Chinese, Japanese and Korean subtitles typically allow fewer characters per line (often around 16–23 full-width characters) because each character is wider and carries more meaning. Languages with long words, such as German, benefit from more careful line breaking. Check the style guide for your target language.

A short worked example

The sentence “You should have told me you were leaving yesterday.” has 52 characters. A viewer reading at 20 characters per second needs 2.6 seconds. If the speaker finishes in 2.0 seconds, there are three options: let the subtitle stay for 0.6 seconds into the following silence (best), start it slightly before the speech if the previous cue allows it, or shorten it to “You should’ve told me you were leaving.” (40 characters, 2.0 seconds). Making this kind of decision hundreds of times is what subtitling is about; the analyser merely tells you where to look.

Checklist before you deliver

• No cue shorter than about 0.8 seconds or longer than 7 seconds.
• No line longer than 42 characters and never more than two lines.
• Reading speed at or below the platform’s limit for the audience.
• No overlaps, no empty cues, no cues out of order.
• Consistent spelling of names, numbers and punctuation (for example, always use the same dash for interruptions).
• File saved as UTF-8 with the correct language code in the file name, such as movie.en.srt.

Frequently asked questions