Because "KB" can mean 1,000 bytes or 1,024 bytes, and your computer and the portal may not use the same one. A file of 203,000 bytes shows as about 199 KB in Windows but is over the limit for a portal that allows 200,000 bytes. If a portal rejects a file that looks like it's under the limit, compress it to about 3% below the limit, for example 195 KB for a 200 KB limit.
Two kinds of kilobyte
- 1 KB = 1,000 bytes (the decimal, SI meaning). macOS Finder counts this way.
- 1 KB = 1,024 bytes (strictly called a kibibyte, KiB). Windows File Explorer counts this way but still writes "KB".
The same file can therefore show two different sizes. A 203,000-byte PDF is 203 KB on a Mac and about 199 KB on Windows.
How portals count
Portals don't say which kilobyte they mean, and different portals are built differently. We can't tell you how each one counts. What you can control is the margin: a file under the stricter reading (1,000 bytes per KB) passes either way.
How CompressKaro counts
CompressKaro aims under the stricter reading, so you can type the portal's own limit. A 200 KB target produces a file of at most 200,000 bytes, and a 1 MB target at most 1,000,000 bytes. That passes a portal that counts 1,000 bytes per KB and one that counts 1,024. The result card only says "under your limit" when the file meets it. Sizes are still shown the Windows way (1 KB = 1,024 bytes), so a file that fits a 200 KB limit can show as about 195 KB.
| Portal limit | Target to type in CompressKaro | Bytes at most |
|---|---|---|
| 20 KB | 20 KB | 20,000 |
| 50 KB | 50 KB | 50,000 |
| 100 KB | 100 KB | 100,000 |
| 200 KB | 200 KB | 200,000 |
| 500 KB | 500 KB | 500,000 |
| 1 MB | 1 MB | 1,000,000 |
| 2 MB | 2 MB | 2,000,000 |
With a tool that counts 1,024 bytes per KB, set the target about 3% below the limit instead (195 KB for 200 KB).
Other reasons a portal rejects a file
- Below the minimum. Many exam forms also have a minimum, such as 10 KB for a signature. Check both ends of the range.
- Wrong format. A PDF where the portal wants JPG, or a .jpeg extension where it wants .jpg.
- Wrong pixel size or DPI for photos and signatures. The portal limits table lists these where we have the official numbers.