QR codes can be different sizes and must be adjusted based on the user’s needs. The minimum recommended pixel ratio is 38 x 38px, and the absolute minimum size is 1 x 1cm (0.4 x 0.4in). However, this size isn’t scannable on all phones, so making the size at least 2 x 2cm (0.8 x 0.8in) for print is advised.
Keep in mind that this is the minimum recommended size, meaning the final size will depend on your printing medium, the larger your marketing material, the larger your QR code has to be. The scanning distance ratio to the QR code sizing should be roughly 10:1. This means if a QR code is scanned from approximately a 100 cm distance, the size of the QR should be at least 10 cm. The size of a QR code on a billboard will have to be bigger than on a business card since the scanning distance is larger.
To ensure the resolution of your QR code when being size-adjusted remains high-quality, make sure to download it as a vector file (EPS, PDF, and SVG).