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.
Thus, the real capacity is
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 110-120GB
There is calculation difference between manufacturer and your PC, please Google 'Memory card capacity' to get more information.