KB or KiB: kilobytes, kibibytes and why the two exist

The same word, kilo, was used for 1,000 and for 1,024. The IEC prefixes were made to end the confusion.

What happened

Early computer engineers noticed that 2^10, which is 1,024, is nearly equal to 1,000, and began to use the SI prefix "kilo" for 1,024. NIST's page on binary prefixes describes this history: people who worked with computers knew that "kilobyte" implied 1,024 bytes in their field, but the same word meant exactly 1,000 everywhere else. As memory and disks grew, the gap between 1,000^n and 1,024^n grew too: about 2.4 percent at kilo, about 4.9 percent at mega, about 7.4 percent at giga and about 10 percent at tera.

The fix: binary prefixes

The International Electrotechnical Commission introduced names for the powers of 1,024. NIST's page lists them: kibi (Ki), mebi (Mi), gibi (Gi), tebi (Ti) and so on, from the words "kilo binary" and so on. One kibibit is 2^10 = 1,024 bits, and one mebibyte is 2^20 bytes.

Who uses what

• Drive and phone makers use decimal units: a 1 TB drive has 10^12 bytes.
• Some operating systems show sizes using 1,024 but with the decimal names, so the same drive appears as about 931 GB.
• Others show decimal units, or the IEC names.
• Memory (RAM) is built in powers of two, so a "16 GB" module is 16 GiB.
• Programmers and documentation increasingly use KiB, MiB and GiB when exactness matters.

How to avoid mistakes

1. When a number matters, find out which system it uses.
2. In your own writing, use KiB, MiB and GiB for powers of 1,024, and KB, MB and GB for powers of 1,000.
3. For a quick estimate, treat them as equal up to GB, then remember the gap at terabyte scale.

Use the byte converter to see the same amount in both systems.

This is an independent guide. It is not connected with the IERS, BIPM, IANA, NIST or any company named here. Facts were read on 14 November 2026 from the sources named on each page; calculated values come from Python.