Taking a look specifically at the Big Bang Theory, up until Season 10, most episodes were around 21 minutes. Season 10 had episodes around 20-21 minutes, and the current season (11) hovers around the 19-20 minute mark.
When I was in High School, our English teacher actually wrote and produced a TV show and was telling us about her experience and some of the things she had to do to cut episodes in the right amount of time for commercials. At the time (mid 2000s), the average was 23 minutes of show per 30 minute episode.
Looking across my library at recent shows, it seems to average about 21 minutes nowadays.
When I was in High School, our English teacher actually wrote and produced a TV show and was telling us about her experience and some of the things she had to do to cut episodes in the right amount of time for commercials. At the time (mid 2000s), the average was 23 minutes of show per 30 minute episode.
Looking across my library at recent shows, it seems to average about 21 minutes nowadays.