QR code size and distance: how big should it be?

Allow roughly one unit of code width for every ten units of scanning distance. A code people scan from 50 cm away should be about 5 cm across; a poster read from 3 m needs something in the region of 30 cm.

Distance is only part of it. Contrast, quiet zone, lighting and whether the surface is glossy all shift the practical minimum. When in doubt, go larger — the cost of extra centimeters is nothing next to a reprint.

Take the scanning distance and divide by ten: that is the minimum code width. Somebody 80 cm away needs a code at least 8 cm across; at 4 m, at least 40 cm.

Then leave the quiet zone alone. The blank border around the pattern should be at least four modules wide, and it is part of the printed area even though it is not part of the code.

Round up. A code slightly too large looks deliberate; one slightly too small looks broken.

A code displayed on a phone or a monitor does not need the same physical size, because backlit glass gives a camera far more contrast than ink on paper. A code filling about a quarter of the screen scans comfortably.

What matters on screen is resolution and placement. Export at a size that stays crisp on a high-density display, keep a clear border, and never sit a code over a moving background or video.