Byte & Storage Unit Converter

Almost everyone has bought a storage device and found less space than the box promised. The shortfall is not a trick or a fault; it comes from two systems of prefixes that share names. This converter keeps them apart: it handles both families, bits as well as bytes, and shows the answer in every unit so the difference is easy to see.

Two families of prefixes

The SI prefixes kilo, mega, giga and tera mean 1,000, 1,000,000, 1,000,000,000 and so on, powers of ten. Computing history used the same words for powers of 1,024, because memory addresses come in powers of two, and for decades a “kilobyte” could mean either. In 1998 the IEC introduced the binary prefixes kibi, mebi, gibi and tebi, with the symbols KiB, MiB, GiB and TiB, to settle the matter. A kibibyte is exactly 1,024 bytes, a mebibyte 1,048,576 bytes and a gibibyte 1,073,741,824 bytes.

Why drives seem to shrink

Drive makers count in decimal: a 1 TB drive holds 1,000,000,000,000 bytes. Windows divides by 1,024 three times and labels the answer “GB”, although it is really GiB, so the same drive appears as about 931 GB. Other operating systems, including macOS, now report decimal units and show the full 1,000. When you pick TB or GB as the source unit, the converter adds a note giving the figure in GiB.

Bits and bytes

A byte is eight bits. Network speeds are quoted in bits per second (Mbit/s or Mb/s), whereas file sizes use bytes (MB), so a 100 Mbit/s link moves 12.5 MB each second at best. The unit list includes both sets, with kbit, Mbit, Gbit and Tbit, and their binary counterparts Kibit, Mibit, Gibit and Tibit. The lower-case b means bit and the upper-case B means byte, in every unit.

Using the page

Enter an amount, select the unit it is in and the unit you want, and read the answer. A table below lists the same amount in every other unit, grouped into decimal, binary and bit units, so you can find the right one without converting repeatedly. The Swap button reverses the choice. Two sample buttons load a common case: a 1 TB drive in GiB and 100 Mbit/s in MB.

A worked example

For the first sample, 1 TB in GiB: 10¹² bytes divided by 1,073,741,824 bytes per GiB is 931.322574615479…, shown rounded and marked as such. The long result is rounded for display after the calculation is done exactly. The same amount is 953,674.31640625 MiB, which shows how the binary figures keep dropping with each step. For the second sample, 100 megabits is 12,500,000 bytes, which is 12.5 MB. A conversion in the other direction, 1 GiB to MB, gives 1,073.741824.

Limits

The converter works with amounts of data, not with rates over time, so it will not tell you how long a download takes; divide the size by the speed in the same unit. It does not apply file-system overhead, compression or the space taken by formatting. Results are exact, but very long decimals are rounded to a readable number of digits and marked as rounded.

Related tools

• UTF-8 Byte Counter measures the size of text in bytes.
• Page Weight Calculator adds up the size of a web page.
• Number Base Converter converts numbers between bases.
• Binary to Decimal explains the powers of two behind the binary units.