Data Sizes
Decimal vs. binary byte quantities — understanding the difference between GB and GiB, and why it matters.
Why 1 GB ≠ 1 GiB
Two different prefix systems are in use for data storage, and they give different values for the same byte count:
- Decimal (SI): 1 GB = 10⁹ = 1,000,000,000 bytes — used by hard drive manufacturers and SI standards
- Binary (IEC): 1 GiB = 2³⁰ = 1,073,741,824 bytes — used by operating systems and memory chips
The IEC standardized binary prefixes (kibi, mebi, gibi, …) in 1998 (IEC 80000-13) precisely to resolve this ambiguity.
Using the correct prefix — GB vs
GiB — removes a common source of confusion in software interfaces and documentation.
Decimal vs. Binary Representations
| Bytes (exact) | Decimal (SI / powers of 10) | Binary (IEC / powers of 2¹⁰) |
|---|---|---|
| 512 | 512 B | 512 B |
| 1,024 | 1.02 kB | 1 KiB |
| 1,000,000 | 1 MB | 976.56 KiB |
| 1,000,000,000 | 1 GB | 953.67 MiB |
| 1,073,741,824 | 1.07 GB | 1 GiB |
Standards: SI decimal prefixes are defined by BIPM. Binary prefixes are standardized in IEC 80000-13 (formerly IEC 60027-2). See Prefixes for the full reference.