Capacity flash memory products are usually shipped in accordance with 1MB = 1000KB, 1G = 1000MB computing,but the operating system using binary arithmetic 1MB = 1024KB, 1GB = 1024MB, so there are some differences between the display capacity and standard capacity memory products.

This is calculation difference between manufacturer and our PC

4GB =approximately 3.6GB-3.8GB
8GB =approximately 7.4GB-7.6GB
16GB=approximately 14GB-15GB
32GB=approximately 28GB-30GB
64GB=approximately 58GB-60GB
128GB=approximately 110GB-120GB
256GB=approximately 230GB-238GB
512GB=approximately 460GB-476GB

The most reliable software to verify memory is H2testw.