Start with the actual rule
Read the upload instruction carefully and copy both numbers. If it says 20–50 KB, a 12 KB image can be rejected even though it is small. A safe result sits inside the range, not exactly on its edge.
Compression and resizing are different
Compression removes image detail to reduce bytes. Resizing changes the pixel grid itself. A very large phone photo may need both: resizing first, then compression to reach the final limit.
Why “exactly 20 KB” is usually the wrong target
File systems and portals can round sizes differently. If the rule allows 20–50 KB, aim comfortably inside it. RulePix reports the finished byte size before download.
Keep the required dimensions in view
A file can pass the KB rule and still fail its pixel rule. Enter the requested width and height at the same time so the downloaded result is checked as one complete file.