SyncMySubsWhat is CPS (characters per second)?
CPS, characters per second, is the standard measure of subtitle reading speed: how much text a subtitle shows against how long it stays on screen. It is the single most common reason a subtitle file fails streaming QC, and it is easy to check before you deliver.
What CPS actually measures
Take the number of characters in a subtitle and divide it by the number of seconds it is visible. A line of 40 characters shown for two seconds runs at 20 characters per second. The higher that number, the less time a viewer has to read the line before it disappears, and past a certain point they simply cannot keep up, especially while also watching the picture. Reading speed is why a subtitle can be a perfectly accurate translation and still be a bad subtitle: the words are right, but they are gone too fast.
Netflix and other platform limits
Streaming platforms publish reading-speed limits, and a file that breaks them gets flagged. Netflix is the one most people ask about, and the honest answer is that there is no single magic number. Netflix's Timed Text Style Guide has set reading-speed maximums in the region of 17 to 20 characters per second for adult content and 13 to 17 for children's content, with the exact figure depending on the guide version and the language.
Those numbers have changed over time and vary by content type and language, which is why you will find different figures quoted confidently across the web. Do not treat any one of them as gospel. For a real delivery, check Netflix's official Partner Help Center for the current spec that applies to your title. Other platforms, including the BBC, Disney+, Amazon, and Apple TV+, publish their own guides with broadly similar but not identical limits, so the same file can pass one and fail another.
How to check and fix your own file
You do not have to eyeball this. Drop your subtitles into the CPS Checker and it flags every cue that reads too fast, so you can see exactly which lines are the problem and how far over they are. To review and adjust reading speed across the file, the Reading Speed tool shows the CPS of each cue and helps you bring the fast ones down, usually by giving a line more time on screen or trimming the wording. Both run entirely in your browser, and your file is never uploaded.
FAQ
What is a good CPS for subtitles?
It depends on the audience and the platform. Many guides treat somewhere around 15 to 17 characters per second as comfortable for adult viewers, with lower limits for children's content. The figure that actually counts is whatever the current guide for your target platform specifies, so check that rather than a general rule of thumb. To see where your file sits, use the CPS Checker.
What is Netflix's subtitle reading speed limit?
Netflix's Timed Text Style Guide has set maximums in the region of 17 to 20 characters per second for adult content and 13 to 17 for children's content, depending on the guide version and language. These numbers have changed over time, so treat any single figure quoted online with caution and check Netflix's official Partner Help Center for the spec that currently applies to your delivery.
Why was my subtitle file rejected for reading speed?
Some cues almost certainly exceed the maximum characters per second in the platform's spec, which QC flags automatically. Find the offending lines with the CPS Checker, then fix them by extending the cue's on-screen time, tightening the wording, or splitting a long line across two cues.
Do spaces count as characters in CPS?
It depends on the guide. Some count every character including spaces, others count differently, so the exact CPS for the same line can vary between specs. What matters is comparing your file against the limit in the guide you are delivering to, using a consistent count throughout.