Subtitle Reading Speed Calculator (CPS & WPM Checker)

Subtitle quality control turns on one number: reading speed. If a line flashes by faster than a viewer can read it, the subtitle fails, and streaming vendors run automated checks that reject cues over the limit. This tool measures reading speed two ways broadcasters use, characters-per-second and words-per-minute, and compares them to the published ceilings.

1. Character count (C).Count every visible character in the cue, letters, digits, spaces and punctuation, but not the line break between two lines. Netflix, the BBC and the EBU all measure the full glyph-and-space count. A two-line cue counts as the sum of both lines' characters.
2. Duration (D). The time the cue is on screen, in seconds. If you paste SRT timecodes, the tool computes D = end − start, parsing HH:MM:SS,mmm to milliseconds.
3. Reading speed. CPS = C ÷ D and WPM = W ÷ (D ÷ 60), where W is the word count (whitespace-separated tokens).
4. Verdict. Compare CPS to the preset ceiling, 17 (Netflix English adult), 13 (Netflix children), 20 (General/EBU) or a custom value. For the BBC preset, the words-per-minute target is converted to an equivalent CPS ceiling using the standard convention that one word ≈ 6 characters (five letters plus a space), and the cue is flagged on both wpm and CPS.
5. Duration bounds. The cue is also flagged if it sits on screen for less than 0.833seconds (Netflix's 5/6-second minimum) or more than 7 seconds (the maximum per event).
6. Recommended minimum duration. Dmin = C ÷ maxCPS, then raised to the 0.833-second floor if shorter. Extending the cue to Dmin brings its reading speed exactly down to the ceiling. This is the single edit that fixes an over-speed line.

The figures are published, stable values from Netflix's Timed Text Style Guides and the BBC Subtitle Guidelines; the tool performs only arithmetic on them. Reading speed alone does not judge line length (characters-per-line) or line count. Those are separate rules, but it is the check most cues fail first.

• Netflix: English (USA) Timed Text Style Guide (17/13 CPS reading speed)
• Netflix: Timed Text Style Guide: General Requirements (5/6 s minimum, 7 s maximum duration)
• BBC: Subtitle Guidelines (words-per-minute reading-speed targets)

The reading-speed and duration limits on this page were last cross-checked against the Netflix and BBC sources on 2026-07-12. They are re-checked on each build; the figures are published, stable broadcaster requirements.