Currently Being ModeratedJan 16, 2013 6:01 PM (in response to designer_02)
You should be able to insert a blank, then in the Finder select the DVD icon and do Get Info (either File > Get Info or command-I (the letter "i")) The Get Info window should tell you how much space there is on the disc.
Most DVDs (DVD-R, DVD+R, DVD-RW, DVD+RW) are nominally 4.5-4.7GB unless you purchased dual-layer DVD media (eg DVD+R/DL) in which case they are nominally 8.5 GB.
Currently Being ModeratedJan 17, 2013 1:40 PM (in response to MartinR)
No dvd icon will show on desktop or finder. Thought of getting info from there already. But did find some old dvds, not my brand now but figured mine now are the standard 4.5-4.7. So thanks for the suggestion anyway.