"A DVD quality movie will typically run to around 4GB, and a Blu-ray movie to 7 or 8GB..."
You're using the wrong codecs then. DVD-quality local rips^H^H^H^Hcopies are around 700MB, and 1080p quality runs around 2-4GB.
Although a few extra bytes are taken up by having ".x265.BDRip-YIFY.EngSubs" and suchlike appended to the filename.
...Or so I've heard.