How to use the subtitle reading speed calculator
A subtitle only works if the viewer can finish reading it before it disappears. The measure for that is CPS, characters per second: the characters in one cue divided by how long the cue stays on screen. Paste a cue and its duration to see the resulting speed, whether it sits under your ceiling, and the minimum duration the cue would need.
The default ceiling of 20 characters per second reflects a figure widely used for adult English subtitling, but it is a default, not a standard. Children's programming is usually held to a much lower speed, and individual clients publish their own style guides. The ceiling box is editable so you can work to the guide you were actually given.
Characters are counted with spaces included, a line break counts as one space, and an emoji counts as one character. The tool also reports how many lines the cue has and how long the longest one is, because most guides cap a cue at two lines and set a maximum line length in characters.
When the speed comes out too high there are only two fixes: hold the cue longer, or rewrite it shorter. Nothing you paste is uploaded.
Frequently Asked Questions
No. It is a widely used working figure for adult English subtitles, kept here as an editable default. Your client or broadcaster style guide takes precedence.
Yes. Spaces are included and a line break is counted as one space. Some guides count differently, so adjust the ceiling to match the convention you work to.