The size of video is determined by the bitrate and the bitrate alone. For example the DV format has a set bitrate of about 25 megabits/s and requires approx 13.5 GB's of space for one hour.
What bitrate a video may be is determined by a few factors most notably.
- Codec used, some codecs compress better than others
- Resolution, the higher the resolution the more bitrate you need.
For example to the average eye the following formats at a resolution of 720X480 and one hour of footage would appear to look almost identical:
Uncompressed: approx 60 GB
DV: 13.5 GB
DVD (MPEG2): Varies, average bitrate used in Hollywood movie is 6 megabit/s which needs about 4GB per hour.
WMV : Varies as well but to achieve quality comparable to DVD you're looking at about 1GB an hour.
So to answer your question it really depends on the bitrate you are using.
What codec and bitrate to choose depends on the what you intend to do with the video and the hardware you are using.