You buy a 1 TB drive, plug it in and your computer reports 931 GB. Nothing is missing: the box and the operating system are using two different definitions of a gigabyte. This converter shows both systems next to each other, decimal units that count in thousands and binary units that count in 1,024s, so you can see exactly where the difference comes from.
It handles bits, bytes and every common prefix up to petabytes and pebibytes. The answer appears as you type, with the same quantity listed in all twelve units. Nothing is uploaded; the arithmetic runs in your browser.
Decimal (kB, MB, GB) versus binary (KiB, MiB, GiB)
A bit is a single 0 or 1, and a byte is 8 bits. Above that there are two families of prefixes. The decimal or SI prefixes follow the metric system: 1 kilobyte (kB) is 1,000 bytes, 1 megabyte (MB) is 1,000,000 bytes, 1 gigabyte (GB) is 1,000,000,000 bytes, and each step up is another factor of 1,000. Drive makers, network speeds and most phone storage labels use these.
The binary prefixes were standardised by the IEC in 1998 to give powers of two their own names: 1 kibibyte (KiB) is 1,024 bytes, 1 mebibyte (MiB) is 1,048,576 bytes, 1 gibibyte (GiB) is 1,073,741,824 bytes, and each step is a factor of 1,024. Memory chips come in these sizes, and Windows File Explorer measures files and disks this way while still printing the labels KB, MB and GB. macOS switched to decimal units in version 10.6, which is why the same file can show a different size on a Mac and a PC.
The gap grows with every prefix: about 2.4 percent at the kilo level, 4.9 percent at mega, 7.4 percent at giga and roughly 10 percent at tera. That is the whole story behind the shrinking drive: 1 TB is 10^12 bytes, which is 931.322574615 GiB or 0.909494701773 TiB.
When to convert data sizes
Checking drive and phone capacity
A 256 GB phone or SSD holds 238.418579102 GiB, and a 2 TB external drive shows about 1.82 TiB in Windows. File systems and preinstalled software take a little more, but the unit difference is the largest part.
Download sizes and internet speed
Broadband is sold in megabits per second, while browsers report megabytes. Since a byte is 8 bits, 100 megabits is 12.5 MB. Enter the bit count, for example 100e6 bits, and read the Megabyte row to see the transfer per second.
Upload limits, memory and quotas
Email attachments, cloud quotas and server memory limits may be quoted in either system. A 4 GB limit set in decimal is only 3,814.69726563 MiB, so a file reported as 3.9 GB in Windows may already be too large.
How the converter works
Every unit is stored as an exact number of bytes: a bit is 0.125 bytes, decimal units are powers of 1,000 and binary units are powers of 1,024. Your value is multiplied into bytes and divided by the target unit, then shown with up to 12 significant digits. Exact results stay exact, so 1 GiB displays as 1.073741824 GB and 1 MiB as 1,048.576 kB.
The From and To menus are grouped under Decimal (powers of 1000), Binary (powers of 1024) and Bits, which makes it hard to pick the wrong family by accident. The All units table below the result uses the same grouping, highlights the current target, and lets you click any unit to switch to it. A short explanation of the two systems sits under the result as a reminder.
Comment utiliser cet outil
- Enter the size in Value, for example 1 for a one-terabyte drive.
- Under From, choose the unit from the label, such as Terabyte (TB) in the decimal group.
- Under To, choose the unit your system reports, such as Gibibyte (GiB) in the binary group.
- Compare the result with what your computer shows, and copy any row from the All units table.
Limitations
- Only the bit is offered in the Bits group. For kilobits or megabits, enter the bit count with scientific notation, such as 100e6 for 100 megabits.
- The converter cannot tell you how much space a file system will reserve. Formatting overhead, recovery partitions and preinstalled apps reduce free space further.
- Labels in software are inconsistent. When a program shows GB, check its documentation to know whether it means 10^9 or 2^30 bytes.
- Exabytes, zettabytes and their binary counterparts are not listed, although very large values can still be typed in petabytes.