How to use the Data Storage Converter
- Enter the size you have.
- Choose whether it is a decimal unit (MB, GB, TB) or a binary one (MiB, GiB, TiB).
- Select the target unit.
- Divide by eight when moving between bits and bytes — network speeds are quoted in bits, files in bytes.
- Use the bandwidth calculator for transfer times rather than raw sizes.
How the calculation works
Two parallel systems exist for the same quantities. The decimal SI prefixes are powers of ten: a kilobyte is 1,000 bytes, a megabyte a million, a gigabyte a billion. The binary IEC prefixes, standardised in 1998, are powers of two: a kibibyte is 1,024 bytes, a mebibyte 1,048,576, a gibibyte 1,073,741,824. Both are correct; they simply measure differently.
The gap widens as the units grow, which is the source of the perennial 'missing space' complaint. At the kilo scale the difference is 2.4%, at giga it is 7.4%, and at tera it is 10%. Drive manufacturers label capacity in decimal terabytes, while Windows reports it using binary maths but labels the result 'GB'. A 1 TB drive genuinely holds a trillion bytes; the operating system divides by 1,073,741,824 and displays 931, and nothing has been lost.
Bits versus bytes adds a second factor of eight. Network and broadband speeds are quoted in bits per second, storage in bytes. A 100 Mbps connection transfers at most 12.5 MB per second before protocol overhead, which typically consumes a further 3 to 8%. Confusing the two is why download times routinely come out eight times longer than a naive estimate suggests.
bytes = value × factor; decimal: kB = 10³, MB = 10⁶, GB = 10⁹, TB = 10¹²; binary: KiB = 2¹⁰, MiB = 2²⁰, GiB = 2³⁰, TiB = 2⁴⁰; 1 byte = 8 bitsSource: IEC 80000-13:2008 binary prefixes; BIPM SI Brochure 9th edition; JEDEC Standard 100B.01.
Worked example
A new 2 TB SSD shows as 1.81 TB in the operating system and you want to confirm nothing is wrong.
- Enter 2 and select terabytes (decimal): 2,000,000,000,000 bytes.
- Convert to tebibytes: 2 × 10¹² ÷ 1,099,511,627,776 = 1.819 TiB.
- The OS displays 1.81 'TB' but is actually showing TiB.
- Formatting and reserved blocks then take a further 1 to 2%.
2 TB really is 1.82 TiB — the drive is the advertised size, and the shortfall is a labelling convention, not a defect.
Frequently asked questions
Why does my 1 TB drive show only 931 GB?+
Because the operating system divides by 1,073,741,824 rather than a billion. The drive holds a full trillion bytes; the displayed unit is really gibibytes.
How many megabytes in a gigabyte?+
1,000 decimal MB, or 1,024 MiB in binary terms. Both answers are given by this converter depending on the units you choose.
Why is my 100 Mbps connection only downloading at 12 MB/s?+
Because there are eight bits in a byte. 100 ÷ 8 = 12.5 MB/s is the theoretical maximum, before protocol overhead.
Which units should I use in documentation?+
Use the IEC binary prefixes (MiB, GiB) when you mean powers of two. It removes all ambiguity and is the standards-compliant choice.
Last reviewed September 1, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.