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
The most reliable software to verify memory is H2testw.