The recommended minimum size will depend on the printing medium. To ensure scannability on most smartphones, the QR code must be at least 2 x 2cm (0.8 x 0.8in) and its minimum pixel size must be at least 38 x 38 pixels. Making the QR code too small might cause several issues, like it being undetectable, decoded incorrectly, or scanned with difficulty. So, make sure to adjust the QR code size according to your printing medium.