Hello Hood!
I do not have any information about webcams, but normally the storage is dependent from number of pixels, depth (z.B. 24 bit), Monocrome (1 Channel) or Color (4 Channels) and frame rate.
If you have a uncompressed signal I think you can calculate it by Pixels x Pixels x Depth x Channels x FPS.
Alternativ you can log date 1 minute and can calculate this for some hours.
Regards
WolfgangZ