Data size converter
Convert between data size units.
A drive sold as 1 TB holds 1000⁴ bytes, which an operating system reports as about 931 GiB. Same disk, different base.
Guide to Data Size Units
Basic units
A byte (B) is the basic unit of digital information, representing 8 bits. Originally a byte corresponded to a single character in a computer, today it's the standard unit for data measurement. All larger units are multiples of 1024 (not 1000), because computers operate in binary. Kilo-, mega-, giga-, tera-, and petabytes are the next levels, each 1024 times larger than the previous one. This convention dates back to the early days of computing and is deeply rooted in computer architecture.
Decimal vs binary system difference
There's an important difference between marketing and computing approaches to sizes. Hard drive manufacturers use the decimal system (1 GB = 1,000,000,000 bytes), while computer operating systems use the binary system (1 GiB = 1,073,741,824 bytes). This explains why a drive advertised as 500 GB may appear as about 465 GiB in the system. International standardization organizations have introduced new prefixes (kibi, mebi, gibi, tebi, pebi) to resolve this ambiguity.
Unit applications
Bytes are ubiquitous today: text documents fit in kilobytes, smartphone photos are several megabytes, and HD movies take gigabytes. In the era of cloud computing and big data, terabytes and petabytes have become the standard for data centers and enterprises. For example, 1 TB can hold about 500 hours of HD video or 250,000 high-resolution photos. 1 PB is already massive capacity, sufficient to store data for an entire university or streaming platform.
Exabytes and beyond
As technology and data generation evolve, new units emerge. An exabyte (EB) is 1,000,000,000,000,000,000 bytes (a quintillion), used to measure global internet traffic. Zetta- (ZB) and yottabytes (YB) are units for future applications and theoretical calculations. It's estimated that global data will exceed 180 zettabytes by 2025. Interestingly, the total capacity of all hard drives worldwide is much less than the amount of data generated each year.
Practical tips
When choosing storage devices or planning disk space, consider the difference between declared and available capacity. Some space is always taken by the file system and software. In daily use, it's helpful to remember that 1 MB is about a million characters of text, 1 GB is about an hour of music, and 1 TB is about 1,300 CDs. In the cloud world, data transfer is often limited, so capacity isn't everything - connection speed also matters.
Why your 1 TB drive shows up as 931 GB
Nothing is missing and nobody is cheating. Drive manufacturers count in powers of ten, operating systems count in powers of two, and the two answers drift apart by 9.1% at the terabyte scale. The gap is arithmetic, not shrinkage.
How it works
- Converts between decimal units (kB, MB, GB, TB — powers of 1000) and binary units (KiB, MiB, GiB, TiB — powers of 1024).
- Shows the same quantity in both systems, which is the only way to see where a 'missing' capacity went.
- Handles bits against bytes, the other place the same number means two different things.
decimal, used on packaging 1 TB = 1000⁴ = 1,000,000,000,000 bytes binary, used by most OSes 1 TiB = 1024⁴ = 1,099,511,627,776 bytes ratio = 1024⁴ ÷ 1000⁴ = 1.0995… so a decimal TB displays as about 0.909 TiB — 9.1% smaller
Worked example
Buying a 1 TB drive and looking at what the operating system reports.
- the box promises 1 TB = 1,000,000,000,000 bytes
- the drive really does contain that many bytes
- the OS divides by 1024 three times to reach gibibytes
- 1,000,000,000,000 ÷ 1024³ = 931.3
- so it displays 931 GB — meaning GiB
Both numbers describe the same drive. The 9.1% gap is fixed in percentage terms but grows in absolute terms: a 4 TB drive shows 3.64 TiB, and a 16 TB drive appears to lose 1.45 TB.
Reading the result
- The confusion is mostly a labelling failure. Windows and most file managers display gibibytes but write 'GB'; macOS and Linux increasingly report true decimal GB, which is why the same drive can read differently on two machines.
- The IEC introduced KiB, MiB and GiB in 1998 precisely to end this ambiguity. Adoption has been partial, so 'GB' still means one of two things depending on who printed it.
- Network speeds are quoted in bits, storage in bytes. A 100 Mb/s connection transfers at most about 12.5 MB/s — a factor of eight that is separate from, and often compounded with, the 1000-versus-1024 gap.
- Formatting genuinely does consume space, but only a little. If a drive reports far below 90.9% of its rated size, the cause is something other than unit conventions.
Common questions
- Am I being short-changed by the manufacturer?
- No. A drive sold as 1 TB contains a full trillion bytes, which is what the SI prefix means. The shortfall appears only because the operating system divides by 1024 while labelling the result 'GB'.
- Does the gap get worse with bigger drives?
- As a percentage it stays at 9.1%. In absolute terms it grows: 0.09 TB missing on a 1 TB drive, 1.45 TB on a 16 TB one — which is why the effect feels much more dramatic on large drives.