My SanDisk USB flash drive shows that 43GB is used when I just copied a 10GB folder after formatting [duplicate]

Solution 1:

You already answered your own question: There are lots of small files in it

Every file on an exFAT volume takes at least one blocksize. So a file of a single byte in size takes at least 4K - a size amplification of 1:4096. You are seing a size amplification of 4.3, which is very plausible with lots of small files.

You can check this hypothesis by packing the files with WinRAR and the zero compression settings, then copy this file to the USB stick.

Solution 2:

When formatting as exFAT, you almost surely chose some large allocation unit (block size) like 128k or 512k. Reformat with the standard 4k allocation units and the problem should go away.