DOFIW MEDIA ACCESSIBILITY TOOLS
Caption Reading Speed Calculator
Calculate characters and words per second, compare a caption with a chosen reading-speed target, and find the display duration or end time needed for comfortable reading.
Enter caption and timing
Accepted: HH:MM:SS.mmm, MM:SS.mmm, or seconds. A comma may replace the decimal point.
Interpret the timing
Enter a caption and valid start and end timecodes.
Timing recommendation
- Minimum duration at target
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- Suggested end time
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- Timing adjustment
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- Lines
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- Results and review prompts will appear here.
INPUTS AND OUTPUTS
What the calculator uses
Inputs
Caption text, start and end timecodes, a target characters-per-second rate, and a preferred maximum line length.
Outputs
Duration, normalized character count, word count, CPS, WPM, line measurements, recommended duration, and suggested end time.
Character count includes letters, punctuation, and single spaces after repeated whitespace is normalized. Line breaks are preserved for line-length checks but count as a single space in CPS.
INTERPRETING THE RESULT
A speed number is not the whole caption
Characters per second
CPS divides normalized characters by display duration. The selected target is an editing threshold, not a universal legal limit.
Words per minute
WPM provides a familiar secondary estimate, but word lengths differ. Caption workflows often use CPS for more consistent timing comparisons.
Suggested duration
The minimum shown is the character count divided by the selected target. It does not add shot-change, synchronization, or minimum-duration rules.
Line checks
More than two lines or a line above your chosen length is flagged for review. Re-segmentation must still preserve natural phrases.
USE CASES
Where timing calculations help
- Review individual WebVTT, SRT, broadcast, or social-video captions.
- Compare alternate wording without uploading subtitle files.
- Estimate a safer end time for a dense caption.
- Check line count and length during manual caption editing.
- Document timing decisions during an accessibility review.
LIMITATIONS
Human caption editing remains essential
- Recommended CPS varies by language, audience, platform, content type, and organizational style guide.
- The calculator reviews one caption at a time and does not check gaps, overlaps, shot changes, or synchronization with speech.
- Word counting is whitespace-based and may not suit languages that do not separate words with spaces.
- It cannot judge meaningful line breaks, speaker identification, sound descriptions, accuracy, or completeness.
- A passing speed does not guarantee accessible media or legal compliance.
PRIVACY
Your caption stays in your browser
All timing and text calculations happen locally. Caption content and timecodes are not uploaded, stored, or sent to an API. Clipboard access occurs only when you copy the report.
FREQUENTLY ASKED QUESTIONS
Questions about caption reading speed
What CPS target should I choose?
Follow the delivery platform or organization’s specification when one exists. Otherwise choose a profile appropriate for the audience and test with representative viewers.
Are spaces included in the character count?
Yes. Repeated whitespace and line breaks are normalized to single spaces for the CPS calculation. The separate line check uses the original line breaks.
Why calculate WPM as well as CPS?
WPM is familiar and useful for comparison, while CPS better reflects variation in word length. Neither measure replaces viewer testing.
Should captions always stay on screen for the suggested duration?
No. The value is the mathematical minimum for the selected CPS. Speech timing, shot changes, adjacent captions, and comprehension may require a different edit.
Are two lines always acceptable?
Two lines are common, but the break should follow natural language units and avoid separating closely related words. Platform rules may differ.
Does the tool read subtitle files?
No. It calculates one pasted caption locally. It does not upload, parse, or modify SRT, VTT, or other files.
This tool is an educational timing aid and does not guarantee WCAG conformance or legal compliance. Learn more from the W3C captions guidance.