as much as it says on itANOTHER OPINION : Compact Disc (CD) can hold 740 MB. Digital Video Disc (DVD) can hold 4.7 GB. Usually says on the disc itself.
There are different sizes of CDs:
120 mm (5 inches) : 650MB/74 minutes or 700MB/80 minutes
80 mm (3 inches) : 185MB/21 minutes
60 mm (2.5 inches) : 50MB/9 minutes