Subtitle reading speed guide
Reading speed is the single most useful metric for judging whether a subtitle is readable. It is measured in characters per second (CPS) — how many characters a viewer must read in the time a cue is on screen.
How to calculate CPS
For a given cue:
CPS = character count / cue duration in seconds
Character count includes letters, digits, spaces and punctuation. Excludes HTML tags. For bilingual or CJK subtitles, count each CJK character as 2 characters (because they take roughly double the reading space of a Latin character).
Target CPS values
Different content types have different targets:
| Content type | Recommended max CPS |
|---|---|
| Children's content | 12 |
| Pre-lingual deaf audiences | 17 |
| General adult content | 20 |
| Fast-paced action | 22 |
| Subtitles for translation | 15–17 |
How CPS is different from WPM
Words per minute (WPM) is another common reading metric. For subtitles, CPS is more useful because:
- CPS is time-based. It measures how fast the eye must move, which is the actual constraint in subtitle reading.
- CPS is character-based. Short, common words read faster than long, unusual ones — but a cue full of short words still has a high CPS if the letters are packed densely.
- CPS is standardized. Almost every subtitle guideline uses CPS rather than WPM.
As a rough conversion, 15 CPS is about 160 WPM for English.
When CPS is too high
If a cue exceeds the target CPS, the viewer cannot read it. This manifests in several ways:
- Viewers miss lines entirely.
- Viewers read subtitles but miss the picture (comprehension drops).
- Viewers experience "subtitle fatigue" and stop paying attention.
Fixing high CPS
Three strategies, in order of preference:
- Compress the dialogue. Subtitle is not a transcript. Remove filler words ("uh", "um", "you know"), use contractions, drop redundant phrases. As long as the meaning is preserved, shorter is better.
- Split the cue. If the dialogue has a pause, split the cue into two shorter cues. This is a great option for fast speech that has natural breaks.
- Extend the cue duration. If the source audio has silence after the cue, extend the end time. This only works if there is genuinely more time available — you cannot extend into the next cue.
When CPS is too low
Low CPS is rarely a problem — subtitles that are easy to read are good. But very low CPS sometimes indicates:
- A cue that is on screen much longer than needed (viewer may find it distracting).
- A cue that is nearly empty (maybe one word for 6 seconds), which is odd pacing.
If a cue has CPS below about 5, consider whether it should be shortened.
Special cases
Bilingual subtitles
When subtitles contain two languages (e.g. English and Spanish on separate lines), CPS calculations become complex. In practice, treat the combined text as one cue and apply the same rules. The English line and the Spanish line each need to be readable in the cue duration.
CJK subtitles
Chinese, Japanese and Korean characters convey more meaning per character than Latin letters. The standard for CJK subtitles is often 6–8 characters per second, which is roughly equivalent to 12–16 CPS in Latin scripts.
Subtitles with sound effects
For SDH subtitles that include sound effect descriptions like [door slams], the reading time is the total across all text including the descriptions. Descriptions can push CPS higher than dialogue alone — plan accordingly.
Measuring CPS in practice
Our Duration Report shows per-cue durations but does not directly compute CPS. To calculate CPS for a specific cue:
- Count characters in the dialogue text (including spaces and punctuation, excluding HTML tags).
- Divide by the cue's duration in seconds.
For a full file analysis, use the Word Counter to get total word count and total runtime — this gives average reading speed across the file. It is not per-cue accurate, but it catches gross over-length issues.