What's the smallest size I can print a branded QR code at?

For anything held up to a phone at arm's length — packaging, table tents, business cards, lanyards — don't go below 2cm × 2cm. Styled QRs with a logo in the center are more sensitive to tiny resolution issues than plain ones, and below that size print imperfections start to swallow dots that matter.

For signs scanned from further away, size scales with reading distance. A useful rule of thumb: 1cm of QR per 10cm of scan distance. A yard sign scanned from 2 metres needs to be printed around 20cm × 20cm to stay reliable.

Two more tips:

• Export as SVG for print. Vector preserves every edge at any size. PNG is fine for digital use but rasterises at a fixed resolution.
• Always scan-test before a run. Print a proof at the smallest size the QR will actually appear on the final piece, and scan it from a couple of angles on both iOS and Android. This catches sizing problems before they end up on thousands of boxes.

See the QR Code Designer guide for the full set of scannability and print-sizing notes.