What is the difference between GB and GiB?

A gigabyte (GB) is 1,000,000,000 bytes under the SI decimal standard. A gibibyte (GiB) is 1,073,741,824 bytes (1024³). GiB is about 7.4 percent larger, which is why a 1 TB drive shows as roughly 931 GiB in your OS.

Why do drive makers and operating systems disagree on size?

Storage manufacturers advertise capacity in decimal units (1 TB = 10¹² bytes), while many operating systems report in binary units but label them with decimal symbols. So a 1 TB drive looks like only about 0.909 TB to the OS.

How many bits are in a byte?

Eight. One byte equals 8 bits. File and storage sizes are usually quoted in bytes, while network and bandwidth rates are usually quoted in bits per second.

What are the IEC binary prefixes?

Kibi (KiB, 1024), mebi (MiB, 1024²), gibi (GiB, 1024³), tebi (TiB, 1024⁴) and pebi (PiB, 1024⁵). They were standardised by the IEC in 1998 to remove the ambiguity of using kilo, mega and giga for powers of 1024.

Does this tool run offline?

Yes. All conversions happen locally in your browser with JavaScript. No data is uploaded, logged or stored.

What is the Data Storage Unit Reference?

Convert data storage sizes across SI decimal units (kB=1000) and IEC binary units (KiB=1024), with bits, bytes and the exact factor between the two standards. It runs free in your browser on Gera Tools, with nothing uploaded.

Data Storage Unit Reference

Name: Data Storage Unit Reference
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Decimal and binary storage units side by side

The same word — kilobyte, megabyte, gigabyte — has meant two different things for decades. SI prefixes (kB, MB, GB, TB) use powers of 1000, matching the way drive manufacturers measure capacity. IEC binary prefixes (KiB, MiB, GiB, TiB) use powers of 1024, matching the way operating systems actually address memory. This reference converts a size into every unit of both standards at once, so you can see exactly how big a difference it makes.

How it works

Every input is first converted to a raw byte count, then divided out to each target unit. SI units divide by successive powers of 1000; IEC binary units divide by successive powers of 1024:

1 kB  = 1,000 bytes              1 KiB = 1,024 bytes
1 MB  = 1,000,000 bytes          1 MiB = 1,048,576 bytes
1 GB  = 1,000,000,000 bytes      1 GiB = 1,073,741,824 bytes
1 TB  = 1,000,000,000,000 bytes  1 TiB = 1,099,511,627,776 bytes

One byte is 8 bits, so the tool also shows the value in bits. All conversions share a single byte base, so the decimal and binary columns are exactly comparable with no chained rounding.

The marketing gap — why your drive looks smaller than advertised

A “1 TB” hard drive contains 10¹² bytes. Operating systems that report in binary units (using GiB, or worse, GB to mean GiB) divide by 1024³ to get about 931 GiB — and then sometimes label that 931 GiB as “931 GB”, adding confusion. The drive is not short-changing you; the prefix means something different at each end of the cable.

Advertised	Bytes	OS reports (binary)
1 TB	1,000,000,000,000	~931 GiB
256 GB	256,000,000,000	~238 GiB
512 GB	512,000,000,000	~477 GiB

The gap grows at larger sizes: kB and KiB differ by only 2.4%, but TB and TiB differ by about 10%.

Where each standard is used in practice

SI (decimal) — powers of 1000:

Hard drive and SSD capacity by manufacturers
Network bandwidth (Mbps, Gbps)
Telecommunications standards

IEC binary — powers of 1024:

RAM addressing and reporting
Virtual machine memory allocation
File system and OS reported sizes

Both used inconsistently:

File size displays in Windows (historically labelled “GB” but computed as GiB)
Cloud storage pricing (increasingly moving to SI)

Practical rules of thumb

File sizes are in bytes; network speeds are in bits per second — divide by 8 to convert speed to bytes.
When writing documentation or specs, write the IEC prefix (GiB, MiB) explicitly to remove ambiguity.
For RAM: a system with 16 GB of RAM has exactly 16 × 1024³ = 17,179,869,184 bytes, because memory is almost always addressed in powers of 2.
For cloud billing: most providers bill in SI units (GB = 10⁹ bytes), so a 100 GB data transfer uses exactly 100,000,000,000 bytes.