The best top-end storage devices SanDisk Extreme microSDXC and microSDHC UHS-I Cards Extreme speeds for faster transfer, app performance, and 4K UHD About capacity: 64GB=approximately 58GB-60GB 128GB=approximately 115GB-119GB This is calculation difference between manufacturer and your PC, please Google 'Memory card capacity' to get more information. Your PC says 1GB = 1.073741824 Billion bytes where Market Defines 1GB = 1.00 Billion bytes. Testing Method: The official factory default speed value is the ideal maximum value, the actual speed test process and the use of the environment-related (such as the use of equipment, different configurations, different types of file storage speed is different, because the type of file, size, size Different and different), so we can not guarantee the actual speed value! The speed show on our link is test by professional instrument, you'd better use 3.0 interface and 3.0 card reader, then you can get a nice speed. How to verify the Capacity and Speed of the memory card? 1). Please use quality USB 3.0 card reader to verify all memory card by H2testw on PC. Real memory card should pass H2testw with no error. 2). Please don't use cheap card reader to test Micro SD card, speed of Micro SD card will be reduced by low quality card reader. 3). Micro SD memory card speed is greatly affected by card reader and the capacity you choose , USB port ect. Low quality device will 100% slow down card speed,1MB=1000KB. Package Contents: SanDisk Extreme Micro SD Card with Retail Package*1