What the Subtitle Reading Speed Checker does
This checker measures how fast every subtitle asks the viewer to read - in characters per second (CPS) and words per minute (WPM) - and flags each cue that is too fast, on screen too briefly or too long, has lines over the character limit, or has too many lines. Pick a published guideline such as Netflix's English adult or children's limits or the BBC's broadcast figures, or set your client's own numbers.
Reading speed is the most common reason subtitles fail a quality check, and it is also the easiest to measure objectively. The page works entirely in your browser on SRT or WebVTT, and tells you for each fast cue how long it would need to stay on screen to meet the limit.
How to use it
- Paste the subtitles or drop an .srt or .vtt file. Files with structural errors still load, but fix those first with the SRT Subtitle Validator if the timing looks strange.
- Choose a guideline preset. The figures and the date they were checked against the published guide are shown under the menu.
- Open Limits to see or change each number. Empty a box to skip that check - for example, the BBC figures use words per minute rather than CPS.
- Press Check reading speed. The chart plots CPS for every cue against the limit, and the table lists every cue with its duration, characters, CPS, WPM and the rules it breaks.
- Sort the table by CPS to tackle the fastest cues first, then download the CSV for your subtitler or QC report.
Reading the results
CPS is visible characters, including spaces and punctuation, divided by the time the cue is on screen. Formatting tags are not counted, and a line break counts as one space - the convention most subtitle editors use.
WPM divides words by minutes on screen; the BBC's guidance is written this way, at 160-180 WPM. Words are sequences of letters and digits, so "don't" is one word and a dash is none.
Needs at least is the shortest duration that brings a too-fast cue within the CPS limit: characters divided by the limit. If the gap to the next cue cannot give that time, the text needs condensing instead.
Worked example: six cues of fast drama dialogue against Netflix English (adult)
The drama example is checked against 20 CPS, 42 characters a line, two lines, a minimum of 5/6 of a second and a maximum of 7 seconds.
Cue 1, "You said you'd be here by eight.", has 32 characters in 1.1 seconds: 29.1 CPS. At 20 CPS it needs 32 / 20 = 1.6 seconds. Cue 2 packs a two-speaker exchange - 26 characters, one space, 8 characters, so 35 - into 1.05 seconds: 33.3 CPS. Cue 3 has 70 characters in 2.6 seconds, 26.9 CPS, and needs 3.5 seconds.
Cue 4, "Right.", reads at a comfortable 10 CPS but is on screen for 600 ms, under the 833 ms minimum. Cue 5 is slow at 4.6 CPS but stays up for 8.5 seconds, over the 7-second maximum. Cue 6 has 73 characters in 3.98 seconds, 18.3 CPS, and passes. So 5 of the 6 cues are flagged, and the file averages 14.3 CPS - which shows why an average alone hides the problem cues.
Formulas and scoring rules
- Characters per second
CPS = characters / (end - start in seconds)Characters include spaces and punctuation; tags removed; line breaks count as one space. Displayed to 1 decimal place.- Words per minute
WPM = words / (duration in seconds / 60)- Minimum duration for the CPS limit
needed ms = ceil(characters / max CPS x 1000)- Time per word
needed ms = words x ms per wordThe BBC suggests about 0.3 seconds per word.
Which guideline should I use?
Use the one your client or platform specifies; their style guide wins. Netflix publishes a guide per language - for English (USA) it sets 42 characters a line, two lines, 20 CPS for adult programmes and 17 CPS for children's. Its general requirements set 5/6 of a second as the minimum and 7 seconds as the maximum duration.
The BBC's guidelines speak in words per minute - 160 to 180 WPM - with 37 characters a line for broadcast because of the teletext heritage, and about 0.3 seconds per word as a rule of thumb. Streaming, broadcast and social video often differ, which is why every limit is editable.
Limitations: what the result does not prove
- It measures speed and layout, not whether a cue is easy to read. A 15 CPS subtitle full of long technical terms can still be hard to follow.
- Guideline figures change. The presets are copied from the published guides on the date shown; check the current guide before a delivery.
- Shot changes, frame-accurate timing and minimum gaps in frames need the video; this page only sees the timecodes.
- Character counting follows the common editor convention. Some platforms count differently, for example ignoring punctuation, so small differences at the limit are possible.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- Netflix Timed Text Style Guide - general requirements - checked 19 Sep 2026
- BBC Subtitle Guidelines - checked 19 Sep 2026
- Netflix English (USA) Timed Text Style Guide
Frequently asked questions
What is a good reading speed for subtitles?
It depends on the audience and the client. Netflix allows up to 20 characters per second for English adult programmes and 17 for children's programmes; the BBC recommends 160-180 words per minute. Slower is kinder to viewers, which is why children's limits are lower.
Do spaces count as characters in CPS?
In the usual convention, yes: spaces and punctuation are part of what the eye has to scan. Formatting tags such as <i> are not counted, and the line break between two lines counts as a single space. The Interpret section spells out exactly what this page counts.
How do I fix a subtitle that is too fast?
Either give it more time - extend it into a gap or start it slightly earlier, as long as it still matches the speech - or condense the text. The table shows the minimum duration each fast cue needs, which tells you whether retiming alone can work.
Why is a very short subtitle flagged when its CPS is low?
Because the eye needs a moment to notice a subtitle at all. A one-word cue on screen for half a second flashes past even though its CPS is low, so guidelines set a minimum duration - five-sixths of a second in Netflix's case.
Can subtitles stay on screen too long?
Yes. Viewers re-read subtitles that linger, and a caption left up after the speaker has stopped looks out of sync. Netflix caps an event at 7 seconds; long speeches are split across several cues instead.
Does this check work for WebVTT captions?
Yes. WebVTT files are read directly, including short MM:SS.mmm timecodes and cue settings. Cue settings such as position are ignored for the speed calculation because they do not change how much there is to read.
Last reviewed by the A2Z.Tools team against the sources listed above.
