Use the same unit as the form
If a portal says the file must be under 300 KB, convert that into MB before checking it in your file manager. If it says 2 MB, convert it into KB before choosing a compression target.
Shard Tools uses the common computer-file conversion where 1 MB equals 1024 KB. That is the convention many operating systems and upload tools use when reporting file size.
Leave a little headroom
A file that appears exactly on the limit can still be rejected if the receiving system rounds differently or adds metadata during processing. For important uploads, aim slightly below the stated maximum.
For example, if a form asks for a PDF under 300 KB, targeting 280 KB or 290 KB is often safer than trying to land exactly on 300 KB.
Convert first, compress second
The converter tells you the number to aim for. Compression tools then do the practical work of reducing an image or PDF toward that target.
Pixel dimensions, page count, image quality, and document readability still matter. A file can fit the size limit while no longer being useful, so always inspect the final output.