Bits vs bytes vs bibytes — the storage-industry ambiguity
Storage vendors sell in decimal terabytes. Operating systems display in binary tebibytes. The 7% gap is the source of the 'missing space' complaint on every new drive.
The bit vs byte distinction (1 byte = 8 bits) is old news. The interesting confusion is the SI-vs-binary prefix collision: is a 'kilobyte' 1,000 or 1,024 bytes? Both, depending on who is writing the label.
The exact factors
1 byte = 8 bits > 1 kB (decimal) = 1,000 bytes > 1 KiB (binary, kibibyte) = 1,024 bytes > 1 MB = 1,000,000 B; 1 MiB = 1,048,576 B (~4.9% larger) > 1 GB = 10⁹ B; 1 GiB = 2³⁰ B (~7.4% larger) > 1 TB = 10¹² B; 1 TiB = 2⁴⁰ B (~9.9% larger)
Who uses which
Storage vendors (SSD, HDD, flash cards): decimal — SI-consistent, larger numbers on the box. Network transfer rates: decimal — a '1 Gbps' link is 10⁹ bits/s. RAM: binary — DIMMs are physically 2ⁿ bytes. Windows file sizes: binary but labels as 'GB' (technically wrong). macOS since 10.6: decimal, labelled 'GB' correctly.
Worked example — 'why is my 1 TB drive only 931 GB?'
1 TB = 10¹² bytes = 1,000,000,000,000 B. Windows divides by 2⁴⁰ = 1,099,511,627,776 to get 931 'GB' (actually GiB). Nothing is missing — Windows is measuring in binary while labelling as decimal. macOS shows the same drive as 1.00 TB because it uses decimal consistently.
Network speeds vs file transfer
'1 Gbps' Ethernet = 10⁹ bits/s = 125 × 10⁶ bytes/s = 119 MiB/s. A 1 GiB file at line speed: 1,073,741,824 / 125,000,000 = 8.59 s minimum. Real-world overheads (TCP, encryption, protocol) typically consume 15–25%, so 10–12 s is realistic. Marketing rarely mentions this.
Why IEC prefixes never caught on
IEC introduced KiB, MiB, GiB, TiB in 1998 to end the ambiguity. Academic and engineering documents use them consistently. Consumer software mostly ignores them because 'megabyte' is a familiar word and 'mebibyte' sounds like a joke.
The five-second recap
Storage vendors: decimal (1 TB = 10¹² B). Windows: binary but labelled wrong. Networks: decimal. Multiply file size by 1.1 to convert TB → TiB, or by 0.91 the other way.
Try the converters mentioned in this article
FAQ
How many bytes in a gigabit?+
1 Gb = 10⁹ bits = 125 × 10⁶ bytes = 125 MB decimal = 119.2 MiB binary.
Is DDR memory sized decimal or binary?+
Binary. A '16 GB' DIMM contains exactly 2³⁴ = 17,179,869,184 bytes = 16 GiB.
Why does an SD card lose space?+
Same reason as a hard drive — decimal label vs binary measurement — plus file-system overhead (FAT tables, allocation, wear-levelling) taking 1–5% of the raw capacity.
This article was written by The Turbo Unit Converter engineering desk (Storage & systems) and last reviewed on 2026-06-30 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.