Storage capacity units — GB (SI) vs GiB (IEC)
SI multiplies by 1000. IEC binary multiplies by 1024. Everyone kept using GB, MB but pointing at different powers.
Storage capacity notation has been ambiguous since the 1970s. Manufacturers report decimal multiples (GB = 10⁹ B). OS tools historically use binary multiples but keep the SI label. The IEC standardised the binary prefixes (Ki, Mi, Gi) in 1999 but adoption remains partial.
The exact factors
Decimal (SI): 1 kB = 10³ B, 1 MB = 10⁶ B, 1 GB = 10⁹ B, 1 TB = 10¹² B > Binary (IEC): 1 KiB = 2¹⁰ = 1024 B, 1 MiB = 2²⁰, 1 GiB = 2³⁰, 1 TiB = 2⁴⁰ > 1 GiB / 1 GB = 1.0737 (7.4% larger); grows to 10% at TB scale
Where each is used
Decimal (GB, TB): storage drive marketing, network throughput, some file managers (macOS since 10.6). Binary (GiB, TiB): most Linux tools, Windows Explorer, RAM capacity (always binary because address lines are powers of 2).
Worked example — 'missing' drive space
A '1 TB' drive holds 10¹² bytes = 9.31 × 10¹¹ / 1024⁴ = 931 GiB. Windows shows 931 GB (labelled GB but computed as GiB). Neither is wrong — they use different definitions of the same abbreviation.
Recap
GB = 10⁹. GiB = 2³⁰. The gap widens 7.4% (GB), 9.5% (TB), 12% (PB).
Try the converters mentioned in this article
FAQ
Why does RAM stay binary?+
Memory address lines are natively powers of 2. A 4 GiB DIMM has exactly 4 × 2³⁰ bytes; there is no decimal equivalent.
Is network throughput SI or binary?+
Almost always SI. '1 Gbps' = 10⁹ bits per second, not 2³⁰.
This article was written by The Turbo Unit Converter engineering desk (Applied metrology & engineering units) and last reviewed on 2026-07-07 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.