KB vs MB: file sizes explained
By the Toolbenchly team ·
Upload forms say "maximum 500 KB", your phone says the photo is "2.4 MB", and your computer might say "2,457 KB". Here is how these units relate, why there are two answers to "how many KB in an MB", and how to check a file's size anywhere.
The basics
- Byte (B): the basic unit of file size.
- Kilobyte (KB): about a thousand bytes.
- Megabyte (MB): about a thousand KB.
- Gigabyte (GB): about a thousand MB.
So a 2 MB photo is about 2,000 KB, which is 40 times more than a 50 KB limit.
1 MB = 1000 KB or 1024 KB?
Both are in use, which causes real confusion:
- Decimal (SI): 1 KB = 1,000 bytes and 1 MB = 1,000 KB. Used by macOS, iOS, Android, storage manufacturers and many websites.
- Binary: 1 KB = 1,024 bytes and 1 MB = 1,024 KB. Used by Windows File Explorer and much older software. Strictly these are "KiB" and "MiB", but they are usually still labelled KB and MB.
The difference is small (2.4%) for KB and grows for larger units. It matters when you are right at a limit: a file of 1,020,000 bytes is "1.02 MB" on a Mac but "996 KB" on Windows. Practical rule: aim a few percent under the limit, for example 190 KB for a 200 KB limit, and the file is accepted whichever definition the portal uses.
Conversion table
| KB | MB (÷1000) | MB (÷1024) |
|---|---|---|
| 50 KB | 0.05 MB | 0.049 MB |
| 100 KB | 0.1 MB | 0.098 MB |
| 200 KB | 0.2 MB | 0.195 MB |
| 500 KB | 0.5 MB | 0.488 MB |
| 1,000 KB | 1 MB | 0.977 MB |
| 1,024 KB | 1.024 MB | 1 MB |
| 2,048 KB | 2.048 MB | 2 MB |
| 5,000 KB | 5 MB | 4.88 MB |
For any other value, the Unit Converter has a data storage category.
How to check a file's size
- Windows: right-click the file → Properties. "Size" is the actual size.
- Mac: select the file and press Cmd+I (Get Info).
- iPhone: in the Files app, long-press → Get Info. In Photos, swipe up on a photo or tap ⓘ (shows the size on recent iOS versions).
- Android: in Files or Gallery, open the file's Details or Info.
- On this site: every tool shows the size of your file before and after processing.
Making a file fit
Photos: use the Image Compressor with a target size, or shortcuts like 100 KB and 1 MB. PDFs: use the PDF Compressor. Both run on your device, so documents are never uploaded.