validate the copy of the file tree from windows to mac

I am trying to copy the contents of a flash drive to my mac box. the content originally came from win and the flash drive is formatted in FAT. I worry that not all the content has been copied successfully. I did not find a way to right click on the flash drive and count the number of items (it works in a directory but not on the flash drive). my goal is to validate that the content of the flash drive is identical to the content on the mac. Is there any way to validate the copy? Is there a way to validate by checksum in a file tree recursively and compare both the source (flash drive) and the destination (mac)?