DVD Capacity

The basic types of DVD (12 cm diameter, single-sided or homogeneous double-sided) are referred to by a rough approximation of their capacity in gigabytes. In draft versions of the specification, DVD-5 indeed held five gigabytes, but some parameters were changed later on as explained above, so the capacity decreased. Other formats, those with 8 cm diameter and hybrid variants, acquired similar numeric names with even larger deviation.
The 12 cm type is a standard DVD, and the 8 cm variety is known as a MiniDVD. These are the same sizes as a standard CD and a mini-CD, respectively. The capacity by surface (MiB/cm²) varies from 6.92 MiB/cm² in the DVD-1 to 18.0 MiB/cm² in the DVD-18.
As with hard disk drives, in the DVD realm, gigabyte and the symbol GB are usually used in the SI sense (i.e., 10⁹, or 1,000,000,000 bytes). For distinction, a gigabyte is normally used in the binary sense (i.e., 1024³ (2³⁰), or 1,073,741,824 bytes), which in SI nomenclature is called a gibibyte (GiB).
Each DVD sector contains 2,418 bytes of data, 2,048 bytes of which are user data. There is a small difference in storage space between + and - (hyphen) formats:

Scan of a DVD 4.5 capacity disc

Capacity and nomenclature
SS = single-sided, DS = double-sided, SL = single-layer, DL = dual-layer

Designation		Sides	Layers (total)	Diameter (cm)	Capacity
					(GiB)
DVD-1	SS SL	1	1	8	1.36
DVD-2	SS DL	1	2	8	2.47
DVD-3	DS SL	2	2	8	2.72
DVD-4	DS DL	2	4	8	4.95
DVD-5	SS SL	1	1	12	4.37
DVD-9	SS DL	1	2	12	7.95
DVD-10	DS SL	2	2	12	8.75
DVD-14	DS SL+DL	2	3	12	12.33
DVD-18	DS DL	2	4	12	15.90