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.