Why the memory of my micro SD card is smaller after being formatted through app?
A part of the micro SD card is hidden partitions which are used for system files. Hidden partitions ensure the isolated storage and security of system files, and help with the high read-write efficiency of your storage card.
Therefore, it shows smaller free capacity than its actual size after using app to format the micro SD card.
If you want to use the entire capacity of your micro SD card, you can reformat the card on a computer with disk management tools.