About the Available Capacity
Due to different capacity algorithms and partial capacity are used for system files, management and performance optimization, so the actual available capacity may be less than the identifying capacity.
Acording to the different algorithms, Mathematically 1GB = 1000MB = 1000x1000KB = 1000x1000x1000 bytes, all the manufactor use this way to mark the capacity.
Example: 256GB = 256,000,000,000 bytes. But in computer algorithm, 256,000,000,000 bytes = 256000000000 / 1024 /1024 /1024 =238.4GB, most of the 256GB micro sd cards will be real 235GB-238.4GB showed in the computer.