SanDisk OTG USB3.1 Type c Flash Drive Mini U Disk 150M/s
32GB = approximately 28GB-30GB
64GB = approximately 58GB-60GB
128GB = approximately 114GB-120GB
256GB = approximately 224GB-240GB
512GB = approximately 460GB-476GB
This is calculation difference between manufacturer and your PC, please Google ‘usb flash drive capacity’ to get more information.
Your PC says 1GB = 1.073741824 Billion bytes where Market Defines 1GB = 1.00 Billion bytes.