If the capacity of your SD card is 64GB or above, you should check if its file format is supported by your card reader.
This is because the file system used by SD cards of 64GB (or above) is exFAT (Extended File Allocation Table), which is a newer file system that some ealier card readers might not support. The system might then not be able to identify the card or send messages for the users to format the card but after the formatting the capacity information would become incorrect.
If you're encountering this situation, please contact the vendor of your card reader to check for its compatibility or try using another card reader.