DVD can be:
Single-sided: 2.6Gb
Double-layered: 5.2Gb
Double-sided: 5.2Gb
Double-sided & double-layered: 10.4Gb
You got the DVD capacities completely wrong.
A DVD can be:
DVD-5 (12cm, SS/SL): 4.38 gig (4.7 G) of data, over 2 hours of video
DVD-9 (12cm, SS/DL): 7.95 gig (8.5 G), about 4 hours
DVD-10 (12cm, DS/SL): 8.75 gig (9.4 G), about 4.5 hours
DVD-14 (12cm, DS/ML): 12.33 gig (13.24 G), about 6.5 hours
DVD-18 (12cm, DS/DL): 15.90 gig (17 G), over 8 hours
DVD-1 (8cm, SS/SL): 1.36 gig (1.4 G), about half an hour
DVD-2 (8cm, SS/DL): 2.48 gig (2.7 G), about 1.3 hours
DVD-3 (8cm, DS/SL): 2.72 gig (2.9 G), about 1.4 hours
DVD-4 (8cm, DS/DL): 4.95 gig (5.3 G), about 2.5 hours
DVD-R (12cm, SS/SL): 3.68 gig (3.95 G)
DVD-R (12cm, DS/SL): 7.38 gig (7.9 G)
DVD-R (8cm, SS/SL): 1.15 gig (1.23 G)
DVD-R (8cm, DS/SL): 2.29 gig (2.46 G)
DVD-RAM (12cm, SS/SL): 2.40 gig (2.58 G)
DVD-RAM (12cm, DS/SL): 4.80 gig (5.16 G)
In this list, the DVD+R sizes are missing, but AFAIR they are nearly identical to DVD-5.
Standard are the DVD-5 and DVD-9 versions. Perhaps you mixed those sizes up with DVD-RAM (which isn't a DVD at all, but rather a MO-disk)
