KB to MB and MB to KB converter, 1000 or 1024
KB to MB: in the decimal (SI) system divide by 1,000, so 2,500 kB = 2.5 MB; if you count in 1,024 as Windows does, 2,500 KiB is 2.441 MiB. Pick the system, type kilobytes and the megabytes follow as you type; MB to KB works in the same box.
Example: File size 2,500 · Direction: KB to MB (kB → MB) · Counting system: Decimal: 1 MB = 1,000 kB (SI) → Answer: 2,500 kB = 2.5 MB. Source: IEC 80000-13 / BIPM SI Brochure – kilo = 1000, binary prefixes kibi = 1024 (KiB, MiB). Updated: .
How it is calculated
Two systems, one abbreviation
There are two ways to read “KB”. In the decimal system of the SI, kilo means 1,000: MB = kB ÷ 1,000, so 1,500 kB = 1.5 MB and 3 MB = 3,000 kB. In the binary system, which memory and older software use, a kilobyte is 1,024 bytes: MiB = KiB ÷ 1,024, so 1,500 KiB = 1.465 MiB and 3 MiB = 3,072 KiB. The IEC introduced KiB and MiB in 1998 to keep the two apart. The selector above switches the whole page, including the chart.
Who uses which
- Drive makers, networks, macOS (since 2009), phones: decimal. A “1 TB” drive holds 1,000,000,000,000 bytes, which Windows shows as about 931 GB, because Windows counts in 1,024.
- Windows Explorer, RAM sizes: binary, but labelled KB, MB, GB.
- Upload limits and email: usually decimal in the documentation (Gmail: 25 MB), but check the exact byte count if a file is rejected.
The floppy that fits neither
The “1.44 MB” floppy disk holds 1,440 × 1,024 = 1,474,560 bytes. That is 1.47 MB in decimal and 1.41 MiB in binary: the label used a mix of both. A file of 1,440 kB is 1.44 MB in the decimal system but 1.406 MiB in the binary one.
How large is that, really?
Plain text takes about one byte per character, so 1 kB holds roughly 1,000 characters. A 3-minute MP3 at 128 kbit/s is 2,880 kB, 2.88 MB. A phone photo of 3,000 kB is 3 MB, and 25,000 kB is the 25 MB attachment limit. A CD-R sold as “700 MB” holds 737,280,000 bytes, which is 737.28 MB in decimal and 703.125 MiB in binary, so that label is a binary figure. The gap between the two systems is 2.4 % for a kilobyte, 4.9 % at the megabyte level and 7.4 % at gigabytes, which is why the difference matters more for big drives than for small files.
For MB and GB see MB to GB; to see how long a download of that size takes use the download time calculator.
Frequently asked questions
How many MB is 1000 KB?
1,000 kB = 1 MB in the decimal (SI) system. In binary counting it is a little less: 1,000 KiB = 0.9766 MiB.
How many KB are in a MB?
1 MB = 1,000 kB in decimal and 1 MiB = 1,024 KiB in binary. Windows shows the binary figure but labels it MB.
How do I convert KB to MB?
Divide by 1,000 (decimal) or by 1,024 (binary). For 2,500 kB: 2,500 kB = 2.5 MB or 2,500 KiB = 2.441 MiB.
Why does Windows show a smaller size than the drive label?
The label counts in 1,000 (decimal) and Windows in 1,024 while still writing GB. A 1 TB drive is 1,000,000,000,000 bytes, about 931 GB in Windows.
Is a KB 1000 or 1024 bytes?
Both are in use. By the SI definition (and the IEC standard) 1 kB = 1,000 bytes and 1 KiB = 1,024 bytes. Older software uses 1,024 for KB.
Sources and legal basis
- IEC 80000-13 / BIPM SI Brochure – kilo = 1000, binary prefixes kibi = 1024 (KiB, MiB)
- NIST – Prefixes for binary multiples (kibi, mebi, gibi)
As of: · Editorial policy
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