Storage unit converter
Convert between decimal (1000) and binary (1024) units and see why your disk seems to lose space.
| Unit | Value |
|---|
Why does my 1 TB drive show 931 GB?
1000 versus 1024: what each unit means
Drive makers use the decimal system: 1 kB = 1000 bytes, 1 MB = 1000 kB, 1 GB = 1000 MB and 1 TB = 1000 GB. Computers work in binary and, by tradition, Windows uses powers of 1024 but still writes "GB". To end the confusion the IEC created binary prefixes: KiB, MiB, GiB, TiB (the "i" stands for binary).
| Decimal (SI) | Bytes | Binary (IEC) | Bytes |
|---|---|---|---|
| 1 kB | 1,000 | 1 KiB | 1,024 |
| 1 MB | 1,000,000 | 1 MiB | 1,048,576 |
| 1 GB | 1,000,000,000 | 1 GiB | 1,073,741,824 |
| 1 TB | 1,000,000,000,000 | 1 TiB | 1,099,511,627,776 |
The gap grows with size: 2.4 % at kilo, 4.9 % at mega, 7.4 % at giga and 10 % at tera. So a 1 TB drive (10¹² bytes) is about 931 GiB, which Windows shows as "931 GB". macOS and many phones use decimal units and show 1 TB as sold; Linux depends on the tool (df -h uses 1024, df -H uses 1000).
Bits and bytes: Mbit/s is not MB/s
Connection speeds (fibre, Wi-Fi) are advertised in bits per second (Mbit/s or Mb/s) while files are measured in bytes. A byte is 8 bits, so a 1 Gbit/s fibre line moves at most about 125 MB/s. Work out the real time in the transfer time calculator.