What is the actual real capacity of a USB flash drive?

What is the actual capacity of a USB flash drive?                             

Flash memory vendors are using decimal arithmetic:1MB = 1000KB,1G = 1000MB

The operating system using binary arithmetic:1MB = 1024KB, 1GB = 1024MB

1GB on computer 10003/10243 ≈0.93B

Here is the different capacity between nominal Capacity and available Capacity, it's only for reference, the actual maybe a little different