When a QR code is published it should be of a size that’s appropriate for the scanning environment it’s being put into. The finished printed size of the QR code will be dependent on:
- The distance between the QR code and the scanning device – which determines the size of the QR code in the viewport of the phone camera
- The size of the dots in the code – the more data you put into the code the smaller the dots become
To effectively scan the QR code it should appear to be at least 1cm (0.4 inches) across in the viewport of the scanning device, and as the distance between the camera and the QR code increases, the size of the QR code will need to increase to compensate.
If you have a QR code on the side of a building it would need to be very large because it’s going to be scanned from a long distance, however if it’s printed in a magazine then the scanning device will be held quite close to it so it can be much smaller.
For most smartphones the relationship between scan distance and minimum QR code size is approximately 10:1 so a 2.5cm (1 inch) QR code printed in a magazine will have a nominal effective scan distance of about 250mm (10 inches), and a QR code on a billboard 20 metres (65 feet) from the where a passer-by would be scanning it would probably need to be about 2 metres (6.5 feet) across. There’s a bit of latitude here depending on the sort of smartphone but 10:1 is a good rule of thumb for a well-lit black and white QR code being scanned front-on.
If you have a poorly lit or obliquely positioned QR code, or a coloured one where the foreground/background colour contrast might not be optimal, you should probably reduce this ratio to 8:1 or less (ie; the QR code size should 1/8th or less of the scan distance). Read more