Difference between du and Finder file sizes
Solution 1:
Difference is in units they use.
du uses BLOCKSIZE=4096 bytes by default (rounded if Human Readable format option -h i.e. df -h)
Finder uses BLOCKSIZE=1000 by default
$du -h /usr/lib/libblas.dylib
4.0K /usr/lib/libblas.dylib
and same in Finder.