Free tool
Data Size Converter
Convert any data size through kilobytes, megabytes, gigabytes, terabytes, petabytes, exabytes, zettabytes and yottabytes, with the 1000 against 1024 difference shown side by side.
Convert any data size through the whole scale, from bytes to yottabytes, in both the decimal units drive manufacturers use and the binary units your operating system reports. The gap between the two is why a new drive always looks smaller than the box said.
Decimal, powers of 1000
What drive and ISP marketing uses. 1 KB is exactly 1000 bytes.
| Unit | Value |
|---|
Binary, powers of 1024
What Windows, Linux and macOS report. 1 KiB is exactly 1024 bytes.
| Unit | Value |
|---|
The missing space on a new drive
Buy a 1 TB drive and the operating system reports about 931 GB. Nothing is wrong and nothing has been stolen. The manufacturer counted 1 TB as one trillion bytes, the decimal definition, while Windows divides by 1024 three times and calls the result GB when it is really GiB. The drive holds exactly what was advertised. Two different definitions are being displayed with the same label.
The gap widens as the numbers grow, because it compounds at every step: about 2.4 percent at kilobytes, 7.4 percent at gigabytes, 10 percent at terabytes and nearly 21 percent by the time you reach exabytes. On a 20 TB drive that difference is close to two terabytes, which is large enough to break a backup plan sized on the wrong figure.
Bits and bytes, the other factor of eight
Internet speeds are sold in bits per second and files are measured in bytes, with eight bits to a byte. A 100 Mbps connection transfers about 12.5 MB each second at best, so a 1 GB file takes around eighty seconds rather than ten. This is not a trick, it is simply two different units with confusingly similar abbreviations: a lower case b is bits, an upper case B is bytes. Most arguments about a connection being slower than advertised dissolve once that single conversion is applied.
The units past petabyte
Zettabytes and yottabytes used to be theoretical and are now quoted in real figures, since global internet traffic passed a zettabyte a year some time ago. Ronnabyte and quettabyte were added to the official set of SI prefixes in 2022, extending the scale to a thousand yottabytes and a million yottabytes respectively. They are included here for completeness. Nobody is storing one yet, and a browser cannot hold numbers that large exactly, which is why they display in scientific notation.