This is calculation difference between manufacturer and our PC, please Google 'Memory card capacity' to get more information.
Understanding speed classes
The SD card association defines card speeds using two terms: Speed Class and UHS Speed Class.
Speed class is the original rating used and the number defines the card speed; 4 for 4MB/s, 6 for 6MB/s. 10 for 10MB/s etc.
UHS (Ultra High Speed) uses minimum write speeds to differentiate the cards; UHS-I Speed Class 1 has a minimum write speed of 10MB/s while UHS-I Speed Class 3 has a minimum write speed of 30MB/s.
Speed based on internal testing; performance may be lower depending on host device, interface, usage conditions and other factors. 1MB=1,000,000 byte
Please don't use cheap card reader to test Micro SD card, speed of Micro SD card will be affected by low quality card reader.
Original sandisk Card *1