Originally Posted by b.greenway
1080p TV shows? I assume you mean 1080i.
It doesn't matter. Resolution has nothing to do with the actual file size. Unless the video is uncompressed (or compressed losslessly), you can make any resolution pretty much any file size you want, within obvious reason. Codecs often have maximum and minimum bitrates, and you can never exceed the bitrate of uncompressed video anyway (although the lossy codecs, of course, don't come close to that). On Blu-ray, you're limited by the maximum bitrate of the format's specification.
And actually, on Blu-ray, 1080i has more information in it, since it has 60 interlaced fields corresponding to 30 frames. 1080p is always 24 frames on Blu-ray. The spec doesn't allow for 1080p video at 30 or 60 fps.
The answer to the original question is: it completely depends on the encode, and only on the bitrate (the codec is irrelevant when it comes to filesize). Some TV shows use VC-1 to get the average bitrate under 20 Mb/s to jam more episodes on a disc, while others use AVC encodes in the mid 30 Mb/s range (still others use AVC in the 20's). At 20 Mb/s, 45 min of video would take up 6750 MB. At 30 Mb/s, 45 min of video takes up 10125 MB.
That doesn't include the audio. Lossless audio takes up 2-4 Mb/s (depending on the codec), while lossy audio can be anywhere. The space taken up for a Dolby Digital track at 640 Kb/s is pretty much nothing in comparison to the video (about 210 MB for 45 min).