What is the maximum size of SD card (How many GBs) can Lenovo Laptop (Y40-80) use?

When using a 64-bit OS, that computer can probably access a single partition that is 18,446,744,073,709,551,616 bits large without any trouble… Regardless of whether it's an internal data storage device or an external data storage device.

I doubt that you'll find an SD card with that capacity configured as a single partition… Yet.

SD cards keep getting bigger and bigger and bigger but you're a Lenovo laptop will recognize whatever SD card that comes out as long as it's formatted with NTFS or FAT32