Change in average ratings for adults 18–49 (2017 vs. 2017):
1) NBC: 2.4, -8%
2) CBS: 1.8, -14%
3) Fox: 1.9, -17%
4) ABC: 1.6, -16%
5) The CW: 0.6, -14%

Change in average ratings for all viewers (2017 vs. 2017):
1) CBS: 9.9m, -6%
2) NBC: 9.0m, -3%
3) ABC: 6.6m, -9%
4) Fox: 6.2m, -14%
5) The CW: 1.8m million, -4%

More. Where TV Ratings Go From Here

Less than 9% of TV households watch one of the 4 major networks on average.

Flashback. Media Use: Smartphones Up, TV Down — With TV Viewers Growing More Selective

% of viewers reached through one primetime spot on each of the big 3 networks:
1) 35 years ago: ≈ 100%
2) Today: 5%

An advertiser would have to buy ads on 135 different TV networks today to equal the reach from major networks 35 years ago!

Buy deep. The audience on TV is massive and it still accounts for 85% of the video spend. Reaching the highest possible % of your audience is going to require a drastically more complex media plan than a few years ago.