I thought the average actual running time of an hour long shows was 42-43 minutes, the reason I ask was that I had watched on DVD the first episode of the 1982 series: Fame that clocked up to 47 minutes. I know that some shows like Fox' Fringe has limited commercial interruptions - I guess there is no definitive answer to this since it appears to vary ALOT from show to show.

Older shows are longer but they realized they can make more money.

Most current shows run 42-43 minutes, like you said. Fringe is a little over 48 minutes. I just picked up the first season of the original Star Trek, and those episodes clock in at about 50.5 minutes.

Fringe and Dollhouse run anywhere from 48-50 minutes because of this new limited commercials plan that FOX experimented with this season with higher advertiser rates. IMO, I don't think we'll be seeing that again next year.

The average used to be 48-50 minutes up until the mid to late 90s when they started to shove in one to two extra commercial breaks, taking it down to 40-42 mins or so.

Half hour shows used to be 24-25 mins, but are now 20-22.

^ '30 Rock' for instance seems really short when viewed in non-commercial mode from my DVR.