Convert MB, GB, MiB and GiB (Decimal vs Binary)

This converter turns decimal megabytes and gigabytes (MB, GB) into binary mebibytes and gibibytes (MiB, GiB), and back: choose the two units, type a value, and the other field updates at once. It explains and quantifies the gap between the capacity printed on the box of a drive, USB stick or phone and the capacity your operating system displays.

Two families of units coexist. The decimal SI prefixes (kilo, mega, giga, tera) are powers of 1,000: 1 MB = 1,000,000 bytes and 1 GB = 1,000,000,000 bytes. The binary prefixes (kibi, mebi, gibi, tebi) were standardised by the IEC in the late 1990s (now IEC 80000-13) and are powers of 1,024: 1 MiB = 1,048,576 bytes and 1 GiB = 1,073,741,824 bytes.

The formulas: GiB = GB × 1,000,000,000 ÷ 1,073,741,824 ≈ GB × 0.931323; GB = GiB × 1.073742; MiB = MB × 0.953674; MB = MiB × 1.048576. Between units of the same rank the gap widens at every level: 2.4% at kilo, 4.9% at mega, 7.4% at giga, 10% at tera. One byte is 8 bits. The double arrow swaps the direction so you can check a result both ways.

For a mental estimate, subtract about 7% from a capacity in GB to get GiB: 500 GB ≈ 465 GiB (exact 465.66). A 1 TB (1,000 GB) drive therefore appears as about 931 GiB in Windows, which counts in binary but labels it "GB". Manufacturers advertise in decimal, which is consistent with SI; the space is not lost, it is just counted with a different unit.

Do not mix up bytes and bits either. Capacities are given in bytes (MB, GB), network speeds in bits per second (Mbit/s, Gbit/s): 1 byte = 8 bits, so 100 Mbit/s is 12.5 MB/s and 1 Gbit/s is 125 MB/s. The decimal kilo is a lowercase k (kB); the binary kilo is KiB. macOS (since 2009) and many Linux tools show decimal sizes, which is why the same drive can display different values on different systems.