QR codes are cheap to produce and expensive to get wrong, because the mistake usually shows up after a thousand flyers have been printed. Four things decide whether a code works in the real world: size, contrast, quiet zone and the amount of data inside it.
Size follows scanning distance
The working rule is that the code’s width should be about one tenth of the distance it will be scanned from. A code on a table card read from 30 cm can be 3 cm across. A code on a window read from 3 m needs to be around 30 cm. When in doubt, print it larger: an oversized code still scans, an undersized one does not.
Keep the quiet zone
The blank margin around a code is part of the code. Scanners use it to find the pattern’s edges. The specification asks for four modules of clear space, which is roughly the width of one of the small squares in the pattern. Designers routinely crop it to save room, and the result is a code that hesitates or fails on older phones.
Dark on light, always
Scanners expect dark modules on a light background. Inverting that, or using two colours of similar brightness, breaks many readers. Coloured codes are fine if the contrast is strong. Avoid printing over photographs, textured stock or anything glossy enough to throw glare across the pattern.
Less data makes a better code
Every character adds modules, and more modules mean smaller squares at the same printed size, which makes scanning harder. Strip tracking parameters, use a short landing page URL, and point at a page rather than a deep link with a long query string.
Static or dynamic
A static code contains the destination itself. It never expires, needs no account, and cannot be changed after printing. A dynamic code contains a short link that redirects, so you can change the destination later and count scans, but it depends on a service that must stay online and is usually a subscription.
For a menu, a Wi-Fi password or a link to your homepage, static is the right choice. For a campaign whose destination may change, or where you need scan counts, dynamic earns its cost. A middle path is to point a static code at a URL you control and change what lives at that address.
Tell people why they should scan
A bare code on a poster gets ignored. A few words of instruction — Scan for today’s menu — makes the difference. Put the destination in human-readable text too, so people can reach it without scanning.
Test before you print
Print one at final size, on the same stock, and scan it with an old phone and a new one, in the lighting the code will actually live in. The QR code generator exports SVG, which stays sharp at any print size, and offers four error correction levels — choose Q or H for anything that will be handled, weathered or partially covered.