Subtitle CPS Calculator

What is CPS in subtitles and what is a good value?

CPS stands for characters per second: the number of characters in a subtitle divided by the time it stays on screen. A subtitle of 60 characters shown for 2.5 seconds has 24 CPS. The higher the value, the less time viewers have to read before the text disappears, and the less attention is left for the picture. CPS is the usual measure of subtitle reading speed; words per minute expresses the same idea in words.

Limits depend on the audience. Netflix allows up to 20 CPS for adult programmes and 17 for children’s programmes, TED uses 21, the BBC works with about 160 to 180 words per minute, which is roughly 17 CPS, and ARD, ZDF and ORF use 15. The limit slider of this CPS calculator covers 8 to 30 with these presets. Spaces are normally counted as characters; a switch leaves them out if your guideline counts differently.

The manual calculator answers the practical questions for one subtitle: is it too fast, how long would it need at the limit, and how many characters fit into the time available. Opening a file gives the wider view: average, median and fastest CPS, the share of subtitles above the limit and a histogram of reading speeds. A filter then shows only the subtitles that are too fast, so you know exactly where to edit.

CPS limits of common subtitle standards

Tips

• If a subtitle is too fast and there is a pause after it, the Subtitle Duration Fixer extends it automatically as far as the next subtitle allows.
• Where there is no room to extend, the text has to become shorter. Rewrite those subtitles in the SRT Editor, which shows the CPS while you type.
• Reading speed and line length are separate limits. Check the characters per line with the Subtitle Character Counter and fix long lines with the Subtitle Line Breaker.
• Look at the percentage over the limit, not only at the average: a comfortable average can hide a handful of subtitles that nobody can finish reading.