DVD space

Why is that a blank DVD is labelled 4.7Gb but then I burn 4.68gb od data it says there is not enough space?

Officially, the IEC would like us all to use megabytes, gigabytes, etc. to mean the SI "marketing" number of bytes (10^6, 10^9, etc), and the ridiculous sounding "mebibytes" (MiB), "gibibytes" (GiB), etc for binary byte counts (2^20, 2^30, etc). The IEC needs a smack.