Data Converter
0.95367432 MiB
- 8,000,000
- b
- 1,000,000
- B
- 1,000
- kB
- 1
- MB
- 0.001
- GB
- 0.000001
- TB
- 976.563
- KiB
- 0.953674
- MiB
The data converter handles both prefix systems side by side: decimal kilobytes and megabytes, where a kilobyte is 1,000 bytes, and binary kibibytes and mebibytes, where a kibibyte is 1,024. Keeping both visible is the point. The gap between them is why a 1 TB drive shows up as 931 GB.
How it works
Two systems exist because computing wanted powers of two while SI prefixes mean powers of ten. The IEC standardised the binary prefixes in 1998 to end the ambiguity, though the old usage persists.
- Decimal (SI): kB = 1,000 bytes, MB = 1,000,000, GB = 1,000,000,000. Used by drive manufacturers and network speeds.
- Binary (IEC): KiB = 1,024 bytes, MiB = 1,048,576, GiB = 1,073,741,824. Used by operating systems reporting memory and file sizes.
- The gap widens with each step: 2.4 percent at kilo, 4.9 at mega, 7.4 at giga, 10 at tera.
- A bit is one eighth of a byte, which is why network speeds in megabits look eight times better than the download speed you observe.
Examples
Why a 1 TB drive shows as 931 GB
Value
1
From
Terabyte (decimal)
To
Gibibyte (binary)
Result
931.32257 GiB
The manufacturer sells 1,000,000,000,000 bytes. Windows divides by 1,073,741,824 and labels the result GB, so the same drive reads as 931. Nothing is missing. The two are counting in different bases.
Megabits against megabytes
Value
100
From
Megabyte (decimal)
To
Bit
Result
800,000,000 b
Eight bits per byte. A 100 Mb/s connection therefore delivers about 12.5 MB/s at best, which is why advertised speeds feel slower than expected.
Frequently asked questions
Why does my 1 TB drive only show 931 GB?
Because the manufacturer counts in decimal and your operating system counts in binary. The drive really does hold 1,000,000,000,000 bytes, but Windows divides by 1,073,741,824 and still calls the result GB. macOS switched to decimal in 2009, which is why the same drive reads as 1 TB on a Mac.
What is the difference between MB and MiB?
A megabyte is 1,000,000 bytes; a mebibyte is 1,048,576. The IEC introduced the binary prefixes (kibi, mebi, gibi) in 1998 specifically to end the ambiguity. Linux tools and RAM specifications generally use them correctly; Windows still labels binary quantities with decimal prefixes.
Why is my 100 Mb/s connection only downloading at 12 MB/s?
Because network speeds are quoted in megabits and file transfers are shown in megabytes, and there are eight bits in a byte. 100 divided by 8 is 12.5 MB/s, which is the theoretical maximum before protocol overhead.
Which system should I use?
Match whatever your audience expects. Storage marketing and network speeds are decimal; memory sizes and most operating system file listings are binary. When it matters, write MiB rather than MB, that is exactly what the binary prefixes are for.