A standard single-layer DVD holds 4.7 billion bytes, not 4.7 binary gigabytes.

A decimal gigabyte contains one billion bytes. A gibibyte contains 1,073,741,824 bytes, so the same byte count produces a smaller numerical value when divided into gibibytes. The distinction is about the size of the measuring unit.

The familiar 4.7 GB figure is a nominal description of a common DVD format, not a claim that every kind of DVD has that capacity. Layer count, the use of one or both sides, and the particular disc format all matter.

Software can make the difference confusing by showing a binary calculation with a label that looks like a decimal unit. Check the actual byte count and the units before concluding that the manufacturer or computer has lost part of the disc.

DVD brought substantially more capacity than a CD while retaining the familiar full-size disc diameter of 120 millimetres. That physical similarity made the format recognizable, but the storage structures and optical requirements were different. Equal outside dimensions do not imply equal data capacity.

The capacity most people associate with a blank DVD belongs to the single-sided, single-layer version. A common dual-layer DVD instead holds about 8.5 decimal gigabytes. Two layers do not simply make the advertised number exactly twice 4.7, because the physical layout and format constraints differ.

The decimal-versus-binary distinction predates DVDs and appears throughout computing. Decimal prefixes scale by powers of one thousand. Binary units scale by powers of 1,024. The dedicated term gibibyte makes the binary meaning explicit, avoiding the ambiguity that arises when both conventions are called gigabytes.

To convert the headline figure, divide 4,700,000,000 by 1,073,741,824. The result is approximately 4.377, which rounds to 4.38 GiB. Working backward with the same definitions returns the original byte count. Conversion changes the number attached to the capacity, not the capacity itself.

For planning a disc burn, compare like with like. If a collection of files is reported in bytes, use the byte count available on the destination disc. If one figure is in GB and another is in GiB, convert them before deciding whether the collection will fit.

The nominal capacity is also different from the space available to an arbitrary set of files. A file system and its organizational structures use some space. The exact usable amount depends on the disc format and how it is prepared, so the rounded label is not a guarantee for a precisely sized folder.

A video running time is a separate question again. The number of minutes that fit depends on video and audio encoding, their bitrates, menus, and other content. A capacity in gigabytes cannot be translated into one universal movie length without assumptions about how that movie is stored.

DVD capacity and CD sampling figures illustrate why units deserve attention. Bytes measure stored data, while samples describe the representation of a signal over time. Even when two displays both describe storage, decimal and binary unit conventions can make the same underlying quantity look different without any change to the medium.