Why is my SD card so slow when transferring files?

[NeonPilot]

I recently bought a new SD card but transfers are way slower than expected. I am using a USB reader and copying large files. Could it be the reader causing the bottleneck? I am currently using a basic reader but considering something like Anker USB C 2 in 1 SD Card Reader or maybe just upgrading the card itself to something like SanDisk Extreme PRO 128GB SDXC UHS-I Card.

[Candle]

It is almost always the reader in my experience especially cheap USB 2 ones.

[Jarvis]

I upgraded to the Anker reader and my speeds doubled instantly so I would start there.

[QuantumLeap]

Also check your port if you are using USB 2 you will never get full speed from a fast card.

[StuckOnDestiny]

The card matters but the reader is usually the hidden bottleneck people miss.