There are 4 different DVD Disc now in market. D9 and D5 is the most common Disc to save Video movies. And the size of them can be a little bit confusing for users. There are basically 4 different DVD Sizes.

DVD-5 (Single Side Single Layer)
D5 holds around 4 700 000 000 bytes and that is 4.37 computer GB where 1 kbyte is 1024 bytes* . DVD+R/DVD+RW and DVD-R/DVD-RW support this format. This is the most common DVD Media, often called 4.7 GB Media. A DVD-5 disc will hold nominally 133 minutes of high quality MPEG-2 encoded video, together with three surround-sound audio channels and four subtitle channels. (Without video compression one DVD-5 disc would hold only about 3 minutes of video).

DVD-10 (Dual Side Single Layer)
D10 holds around 9 400 000 000 bytes and that is 8.75 computer GB. DVD+R/DVD+RW and DVD-R/DVD-RW support this format. A DVD-10 disc will hold a nominal 133 minutes on each side (ie 266 minutes in all), but the disc needs to be turned over to play the other side.

DVD-9, (Single Side Dual Layer)
D9 holds around 8 540 000 000 bytes and that is 7.95 computer GB. DVD+R support this format. This media is called DVD+R9, DVD+R DL or 8.5 GB Media. A DVD-9 (dual layer) disc and hold 240 minutes of continuous video.

DVD-18, ( Dula side Dual Layer )
D18 holds around 17 080 000 000 bytes and that is 15.9 computer GB. DVD+R supports this format. DVD -18 can hold 240 minutes on each side and the disc needs to be turned over to play the other side.

DVD+R/DVD+RW/DVD+R DL and DVD-R/DVD-RW exact sizes
DVD-R/DVD-RW = 4 706 074 624 bytes ( 4488 MB )
DVD+R/DVD+RW = 4 700 372 992 bytes ( 4482 MB )
DVD+R DL = 8 547 993 600 bytes ( 8152 MB )

Wondershare Mac DVD Copy now can suppot Copy D5 to D5,D9 to D9,D5 to D9, but can not Copy D9 to D5, because there are losing during the backup process. Now the product has upgraded to DVD Copy Pro, you can learn to compress D9 to D5. Most important, this DVD Copy for Mac software is quite easy to use and it takes only a few steps to copy the entire DVD, even able to remove DVD protections with high quality, almost no losing.
you can learn more details from "Mac DVD Copy Software "

Mac DVD Copy Related Tutorials - Copy DVD with Mac the Ripper, Burn ISO Files on Mac...