QR code not scanning? Work through this list

A QR code that won't scan is rarely mysterious. In practice the cause is one of about a dozen things, and they're quick to check once you take them in the right order: print first, file second, destination last. Start at the top, stop when something matches, and the fix will be sitting right next to the cause.

Print problems

Most failures happen between the file and the paper, so check the physical code before anything else.

• Too small. Divide the scanning distance by ten: a code read from 25 cm, like a business card, needs about 2.5 cm; a poster read from two meters needs about 20 cm. Dense codes need more than that.
• No quiet zone. The white border around the code is part of the standard, four modules wide. Designs that crop right up to the edge confuse scanners even when the code itself is intact.
• Low contrast. Light gray on white, brown on beige and pastel combinations fail under shop lighting even when they look fine on a screen.
• Inverted colors. A light code on a dark background reads fine to your eye and fails in many scanner apps. Keep the code darker than its background.
• Glare. Glossy lamination and plastic menu sleeves under a spotlight blind the camera. Matte finishes scan better.
• Curves and folds. A code wrapped around a bottle or printed across a crease loses its geometry. Put codes on flat panels.
• Wear. Scratches, stains and sun fade eat into the error correction budget. A code that scanned in January can be dead by June.

File problems

If a fresh print fails too, the exported file is the suspect.

• You printed a file you never tested. Always scan the exact PNG, SVG or PDF you exported, not the preview on screen.
• Screenshot rot. A code that's been screenshotted, sent through a chat app and screenshotted again has blurred module edges. Go back to the original export.
• An oversized logo. Anything covering more than roughly 20 percent of the code needs H error correction, and even then it's a gamble.
• Upscaled raster. Stretching a small PNG to poster size produces mush. Export at the final size or use the SVG.

Destination problems

When the scanner reads the code but the result disappoints, the code is fine and the data isn't.

• The page moved or died. The code still opens the old URL faithfully; nobody told the URL.
• A login wall. The link works on your phone because you're signed in. Test it from a logged-out browser.
• A finished trial. If the code came from a service and now opens an upgrade page, it was dynamic and the redirect got switched off. The static vs dynamic guide covers why.
• A WiFi typo. Network names and passwords typed from memory are the most common reason WiFi codes fail. Copy them from the router settings and mind the capitalization.

The two-minute test that prevents all of this

1. Print one sample at the final size on the final material.
2. Scan it with two phones, one of them a few years old, from the real distance in the real lighting.
3. Follow the result to the end: page loads, network joins, contact saves.
4. Only then print the full run.

Common questions