A QR code that doesn't scan is worse than no QR code at all — it's a broken experience and wasted print budget. Whether you're putting a code on a business card or a highway billboard, the scan success rate is determined by math and contrast, not luck.

The 10:1 rule for sizing

The most common question: "How big should my QR code be?" The answer depends entirely on how far away people will be when they scan it.

Examples:

• Business card: Held about 10 inches away. (10 ÷ 10 = 1 inch.) Use 1 × 1 inch as a minimum. For vCard codes, use 1.5 inches — they're denser.
• Restaurant table tent: Guest seated, scanning from about 20 inches. (20 ÷ 10 = 2 inches.) The code should be 2 inches wide.
• Storefront poster: Pedestrian on the pavement, scanning from 50 inches away. (50 ÷ 10 = 5 inches.) Code must be at least 5 × 5 inches.
• Highway billboard: Passenger scanning from 60 feet (720 inches). (720 ÷ 10 = 72 inches.) That's a 6-foot square code — which is normal for a billboard format.

Density: the factor the 10:1 rule assumes away

The 10:1 rule works for simple codes like short URLs. The more data you pack into a static code, the more modules (tiny squares) the matrix creates, and the smaller each one gets.

A vCard QR code with a name, title, company, phone, email, and website is significantly denser than a short URL. On a cheap phone camera, those tiny modules can blur together and the scan fails.

Contrast rules

The scanner reads contrast, not colour. It looks for the difference between dark and light areas to identify the finder patterns and decode the data.

The quiet zone

The blank border around the code (the "quiet zone") must be at least four modules wide on all four sides. This is specified in ISO 18004. If you place text or graphics right up against the code matrix, the scanner will misread the edges and the scan will fail.

Physical material traps