According to the Pew Research Center’s State of the Media Report for 2016, 21% of respondents said they had listened to a podcast in the past month. That’s up from 17% in 2015, and was only 12% in 2013. Listening is also moving over towards mobile – they say 65% of those who listen to podcasts say they most often do it on a mobile device. (Makes sense – almost all of my listening is during walks or while driving.) Only about half of the respondents were familiar with the term “podcast” so there is still lots of room for audience growth.
The amount of time listening to podcasts make up only 2% of the time spent consuming audio – compared to 54% of the time spent listening to AM/FM radio.
There are more details at http://www.journalism.org/2016/06/15/podcasting-fact-sheet/.