Below is information about the capacity of DVD disks.

Single layer DVD-5

Holds a maximum of 4,713,749,248 bytes
At an average bit rate of 4.5 MBS has the playback capability of 133 minutes per side.
Directorsite recommends safely fitting 115 minutes at good quality, and a maximum of 145 minutes.

Dual Layer DVD-9

Holds a maximum of 8,565,015,680 bytes (4,282,507,840 bytes per layer).
At an average bit rate of 4.5 MBS a dual layer DVD disk has the playback capability of 240 minutes per side.
Directorsite recommends safely fitting 180 minutes at good quality, and a maximum of 215 minutes.

DVD-R

4.7 DVD-R safely holds 100 minutes at good quality, and a maximum of 115 minutes.
3.95 DVD-R safely holds about 100 minutes.

Please consider additional material on the disk will effect space for video material.
This includes any ROM content, motion graphics, subtitles, additional audio streams, etc.