KB and KiB are not two spellings for the same quantity. KB is decimal; KiB is binary. The difference grows as the unit becomes larger.
Decimal storage units
SI-style storage prefixes use powers of 1,000.
- 1 KB = 1,000 bytes
- 1 MB = 1,000,000 bytes
- 1 GB = 1,000,000,000 bytes
- 1 TB = 1,000,000,000,000 bytes
Binary storage units
IEC binary prefixes use powers of 1,024.
- 1 KiB = 1,024 bytes
- 1 MiB = 1,048,576 bytes
- 1 GiB = 1,073,741,824 bytes
- 1 TiB = 1,099,511,627,776 bytes
Why reported drive capacity can differ
A manufacturer may label capacity using decimal gigabytes while software reports a binary quantity. Filesystem formatting, recovery partitions, and reserved space can reduce usable capacity further.
Worked conversion
One decimal gigabyte is 1,000,000,000 bytes. Dividing by 1,073,741,824 bytes per GiB gives approximately 0.9313 GiB.
Formula
1 GB ≈ 0.9313 GiBUse the correct symbol
Use B for byte and b for bit. Data-transfer rates often use bits per second, while file sizes commonly use bytes.