How much data can you fit in a
single-layer disc can hold 25GB.
A dual-layer disc can hold 50GB.
To ensure that the Blu-ray Disc format is easily extendable
(future-proof) it also includes support for multi-layer discs,
which should allow the storage capacity to be increased to
100GB-200GB (25GB per layer) in the future simply by adding more
layers to the discs.