A Single Layer DVD will fit 4.37GByte of data, where Giga = 1024*1024*1024.
For marketing purposes the capacity of a blank DVD is listed as 4.7GByte, where Giga = 1000*1000*1000.
All burning applications that I know of use the first definition of Giga, so 4.39GByte is more than you can fit on a single (Single Layer) DVD, at least without overburning which very few drives can do (unlike for CD-R overburning).
In other terms the capacity of a blank DVD is:
DVD-R/RW: 4489 MByte (Mega = 1024*1024)
DVD+R/RW: 4483 MByte (Mega = 1024*1024)