How many words per minute should subtitles use?
About 160–200 WPM for adult viewers. Children's content drops to ~140 WPM. WPM is a sanity check; CPS is the primary metric.
Detail
Words per minute (WPM) is the more intuitive but less consistent reading-speed metric. Most adults read silently at 200–300 WPM; subtitles aim lower because the viewer is also watching the video. The major broadcaster CPS caps translate to roughly 160–200 WPM for adult content. Children's content lands at ~140 WPM. WPM is most useful as a sanity check on top of a CPS measurement — if your CPS is on target but WPM looks extreme, you may have unusually short or long words skewing the metric.
17 CPS for adult English content (Netflix). 15 CPS for the BBC. 12 CPS for children's content. Short-form social can push to 20 CPS.
A heavy sans-serif. Inter Black, Montserrat Black, and Anton are reliable defaults. Avoid thin fonts — they break apart on compressed video.