a 1GB flash drive will never be 1GB. The formatted capacity is always less than whats advertised. This is due to file-system overhead and shady marketing.
They market a 1GB as 1,000,000,000 bytes (usually says so in fine print somewhere on the package). When in reality 1 GB is 1,073,741,824 bytes.
They do the same with CDs. To them 1MB= 1,000KB when its actually 1,024KB.