It's all about what you're going to do with the QR code image once you created it. Where are you going to place the QR code? What will the scan distance be?
Minimum Size QR Code
Generally, the recommended minimum size for a QR code is 1 x 1 inch (2,5 x 2,5 cm). This size ensures that most smartphone cameras can easily recognize and decode the QR code without any issues.
The distance between the QR code and the scanning device plays a significant role in determining the minimum size.
As a rule of thumb, the ratio of the scanning distance to the QR code size should be approximately 10:1. This means that if the scanning distance is 10 inches (25,4cm), the QR code should be at least 1 inch (2,5cm) in size.
Roughly divide the average scan distance by 10.
The device used for scanning
Different devices have varying camera resolutions and scanning capabilities. While most modern smartphones can easily scan a 1-inch (2,5cm) QR code, older devices or those with lower-resolution cameras may struggle with smaller QR codes.
Quality of the QR code print
The clarity and contrast of the QR code print can also impact the minimum size. A high-quality print with sharp edges and good contrast between the black and white modules will be easier to scan, even at smaller sizes.
If you know your QR code is going to be small keep the dots black and the background white.