Decimal and binary units
Decimal units step by 1,000: a kilobyte is 1,000 bytes and a gigabyte is 1,000,000,000. Binary units step by 1,024: a kibibyte is 1,024 bytes and a gibibyte is 1,073,741,824.
Storage makers quote decimal units. Many operating systems report binary units while still printing the letters GB, which is where the missing space appears to go.
Worked example
One gigabyte is 1,000,000,000 bytes. That is 953.6743 mebibytes, so a 1 TB drive shows about 931 GiB in a file manager. The gap grows with the size of the unit: it is 2.4 per cent at kilo, 4.9 per cent at mega, 7.4 per cent at giga and 10 per cent at tera.
Bits are eight to a byte, so a 100 Mbps connection delivers 12.5 MB per second at best.
When each unit is correct
Use decimal units for storage capacity, network throughput and anything a manufacturer quotes. Use binary units for memory, file sizes shown by an operating system and anything a program allocates.
The distinction is a standard, not a preference: the IEC defined KiB and MiB in 1998 so that the two could be told apart.
Limits of this calculator
It converts the numbers only. It does not account for filesystem overhead, compression, parity, or the difference between a drive's capacity and the space available after formatting.
For the time a transfer takes at a given speed, use the download time calculator.
For how long a transfer of this size takes, use the download time calculator.
Inputs for the data calculator
Amount
The number you want to convert, in the unit you select below.
From unit
The unit your figure is already in. Storage is usually decimal, memory binary.
To unit
The unit you want the answer in. The result also shows the other convention.
CALCULATOR QUESTIONS
Data calculator questions
Why does my 1 TB drive show 931 GB?
The drive is 1,000,000,000,000 bytes. A system reporting binary units divides by 1,073,741,824, which gives about 931.
Is a megabyte 1,000 or 1,024 kilobytes?
Both are used. 1,000 is the SI decimal value and 1,024 is the binary value, properly called a mebibyte.
How many bits are in a byte?
Eight. Network speeds in megabits per second divide by eight to give megabytes per second.
Does this include formatting overhead?
No. A formatted drive holds less than its raw capacity, and this page converts raw numbers only.