About REAL Capacity
16GB= approximately 14GB-15GB
32GB= approximately 28GB-30GB
64GB= approximately 58GB-60GB
128GB = approximately 119GB-120GB
This is calculation difference between manufacturer and your PC, please Google 'Memory card capacity' to get more information.
For your reference
Your PC says 1GB = 1.073741824 Billion bytes where Market Defines 1 GB = 1.00 Billion bytes.