Most manufacturers of hard disk drives and flash-memory disk devices define 1 gigabyte as 1,000,000,000 bytes so a 32 GB flash drive will have a capacity of 32,000,000,000 bytes. However filesystems define 1 gigabyte as 1,073,741,824 bytes, so 30 GB of files would occupy 32,212,254,720 bytes, so they might not fit.