Differences in size of folder reported on Mac and Synology?

I copied over a folder with my movies on it from a USB drive to my Synology 411j.

All seemed to go well but when I compare the total size in finder it gives different totals.

On the USB drive it shows 323 items and total size of 733.48GB. On the synology it shows the same 323 items but a file size of 730.44GB.

Did some files not copy correct or are there other issues. I read that Windows and Mac's reports file sizes different with regards to how they classify a gigabyte, is something similar at work between the Synology and the Mac?

 

Thanks for the reply. Actually it turns out a few files in a subdirectory didn't copy completely. I used a app called Delta Walker and it compared the files inside the folder and located the problem files. Now my question is why the copy didn't throw any errors yet the files didn't copy correct.

I looked at other folders I copied, thought they are smaller, and they are identical in size. Seems they both report space using the same format.