KB to MB Converter
Convert kilobytes to megabytes and back for file sizes, attachments and upload limits, using the binary (1,024) or decimal (1,000) convention, with the exact byte count.
1 MB = 1,024 KB (binary) or 1,000 KB (decimal)
Divide by 1,024 or by 1,000?
Two conventions share the same labels. In the binary convention, used by Windows and for memory, each step is 1,024 (2¹⁰), so 1 MB is 1,024 KB. In the decimal convention, used by macOS, iPhones, Linux desktops and storage manufacturers, each step is 1,000, matching the SI prefixes. The same file is a slightly different number of "MB" depending on which one you use. Neither is wrong, as long as you know which you're reading.
KB to MB Table in Both Conventions
The two columns differ by 2.4% here. Measured in bytes, the gap grows with each step up: a MiB is 4.9% bigger than a MB, and a GiB 7.4% bigger than a GB.
| KB | MB (÷1,024) | MB (÷1,000) |
|---|---|---|
| 100 KB | 0.0977 | 0.1 |
| 256 KB | 0.25 | 0.256 |
| 500 KB | 0.4883 | 0.5 |
| 512 KB | 0.5 | 0.512 |
| 1,000 KB | 0.9766 | 1 |
| 1,024 KB | 1 | 1.024 |
| 2,048 KB | 2 | 2.048 |
| 2,560 KB | 2.5 | 2.56 |
| 5,000 KB | 4.8828 | 5 |
| 5,120 KB | 5 | 5.12 |
| 10,240 KB | 10 | 10.24 |
| 25,600 KB | 25 | 25.6 |
Why Windows and Mac Show Different Sizes
Copy a 3,450,000-byte photo from a Mac to a PC and its size seems to change from 3.45 MB to 3.29 MB. The file is identical. Each system just divides by a different number:
| Where | Divides by | Notes |
|---|---|---|
| Windows File Explorer | 1,024 | Binary sizes labelled KB, MB, GB |
| macOS (since 10.6) and iOS | 1,000 | Decimal sizes labelled KB, MB, GB |
| Most Linux desktops (GNOME, KDE) | 1,000 or 1,024 | Decimal by default, or binary with KiB, MiB labels |
| Drive and memory-card packaging | 1,000 | Decimal, so a "1 TB" drive holds 10¹² bytes |
Worked Example: Will This Photo Fit a 5 MB Upload Limit?
Windows shows a photo as 4,950 KB. A form says "maximum 5 MB". Will it upload?
Step 1: Get the exact size in bytes (Windows uses binary)
Step 2: Compare with both readings of "5 MB"
It depends on the site. If the limit is decimal, the photo is 68,800 bytes over. When a file is this close, check the exact byte count in the file's properties, or compress it slightly so it's under both.
KiB and MiB: the Unambiguous Names
In 1998 the International Electrotechnical Commission introduced separate names for the binary units: kibibyte (KiB, 1,024 bytes), mebibyte (MiB, 1,024 KiB) and gibibyte (GiB). Under that standard, KB and MB strictly mean 1,000 and 1,000,000 bytes. Linux tools and technical documentation often use KiB and MiB, but most everyday software still writes KB and MB for both, which is why this converter lets you choose.
KB vs Kb: Bytes and Bits
Capital B means bytes and lowercase b means bits, and one byte is 8 bits. File sizes are in bytes (KB, MB), while network speeds are usually in bits (Kbps, Mbps). So a 1 MB file takes at least 8 seconds to send over a 1 Mbps connection, not 1 second. This converter works in bytes only.
Frequently asked questions
Is 1 MB 1,000 KB or 1,024 KB?
Both are in use. Windows and RAM use 1,024. macOS, iOS, most Linux desktops and storage makers use 1,000. The converter supports either.
How many KB is a 25 MB email attachment limit?
25,000 KB (decimal) or 25,600 KB (binary). Email also encodes attachments, which adds about a third, so the file you attach must be smaller than the limit.
Why does my file look bigger on a Mac?
macOS divides by 1,000, so the same number of bytes shows as a slightly larger MB figure than on Windows, which divides by 1,024.
What does 0.5 MB equal in KB?
512 KB in binary, or 500 KB in decimal.
Sources
- NIST: Prefixes for binary multiples: the IEC kibi-, mebi- and gibi- prefixes and their values.
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