Commercial breaks are set by the format-broadcast ‘hours’ especially during prime-time (tv) or drive time (radio) have specific formats for the programming.

Typically a one-hour television show is actually 40–45 minutes in length, and in 4 ‘parts. This allows for four breaks during the hour.

In radio broadcasting most radio programs have 20 minute segments, 15 minutes for content/program, and 5 minutes for commercials. However, with the caveat that many radio and TV news formats now fall outside of that format (think CNN or news-only radio stations).