Read the size and dimensions together
An application may ask for both a file under 100 KB and a photo with a particular width and height. If the form says 600 × 600 pixels, prepare a square at those dimensions before compressing and compare the output with both requirements.
Use the correct input file
Choose the actual JPEG from your device. Changing a PNG or HEIC filename to end in .jpg does not convert it. If the source is a different format, export it as a JPEG with your photo editor first.
Inspect the downloaded JPEG
The tool uses 1,000 bytes per KB. Enter 100 for a 100,000-byte limit or 200 for a 200,000-byte limit. If a 900 × 900 photo becomes 720 × 720 after compression, check whether the destination accepts the smaller dimensions. Open the file at its normal size to make sure important detail remains legible.
If the portal still rejects it
Read the rejection message before trying again. The portal may be checking pixel dimensions, the filename, or photo composition in addition to size. This tool checks the JPEG and file-size ceiling. Those other requirements come from the destination.