What a QR code actually stores
A QR code stores a short piece of text — usually a web address, but it can also be plain text, a Wi-Fi login, contact details, or a payment instruction. The pattern is a grid of dark and light modules; the phone's camera reads the grid, decodes the pattern into that text, and then acts on it. The code itself does not contain a website, an image, or an app — it contains the instructions for finding them.
That distinction matters for size. A short link fits in a small, easy-to-scan code, while a long address needs a denser grid with smaller modules, which is harder to scan from a distance or in poor light. If your code looks crowded, shorten the link first — a URL shortener, or a clean page on your own site, usually makes a visibly simpler code.
How a phone reads the pattern
Three large squares in the corners tell the camera where the code is and which way up it is, which is why a QR code scans at an angle and even upside down. Smaller alignment patterns help the camera cope with curved or tilted surfaces, such as a bottle or a poster that is not quite flat. Error correction is built in: part of the code is redundant data, so a code with a small logo in the middle, a smudge, or a torn corner can often still be read.
Error correction has limits. Covering too much of the code, printing it too small, or using low contrast — such as light grey on white — will break scanning long before the pattern looks damaged to the eye. Dark modules on a light background, with a clear quiet zone of empty space around the code, remain the most reliable combination.
Static vs dynamic QR codes
A static QR code contains the destination directly: scan it, and the phone goes straight to that address. It cannot be changed afterwards, but it never expires on its own and needs no service in between. A dynamic QR code contains a short redirect link managed by a service, so the destination can be changed later and scans can be counted — at the cost of depending on that service staying online and, often, paying for it.
For a printed menu, a business card, or a poster that will not change, a static code is usually the right choice: simple, free, and permanent. For a marketing campaign where the destination might change or you need scan statistics, a dynamic code may be worth it — but check what happens if you stop paying, and whether the redirect service could one day show its own page instead of yours.
Design and printing tips
Print size matters more than most people expect. As a rough rule, a code should be at least about 2 centimetres wide for scanning at close range, and larger in proportion to the viewing distance — a poster meant to be scanned from two metres away needs a much bigger code. Test the printed code with several phones, in the actual lighting, before printing hundreds of copies.
Keep contrast high and avoid placing a code over a busy photograph or a patterned background. If you add a logo in the centre, keep it small — roughly the middle fifth of the code — and test afterwards, because a large logo eats into the error-correction margin. Always include the destination in plain text nearby, so people who cannot or do not want to scan still know where the code leads.
Using QR codes safely
A QR code hides its destination until you scan it, which is exactly what makes it useful for phishing. A sticker placed over a legitimate code can redirect to a fake login page, and a code in an unexpected email or message deserves the same suspicion as an unexpected link. Before entering passwords or payment details, check the address the phone shows after scanning, and type sensitive addresses yourself when in doubt.
As a publisher, the same caution applies in reverse: only link codes to pages you control, keep those pages secure, and do not use a QR code as the only way to reach essential information. A phone number or a short web address printed beside the code costs nothing and helps everyone, including people without a camera phone.
Try the related tools
Try the QR Code Generator on Daily Tools. Try the Color Picker on Daily Tools. Try the Image Resizer on Daily Tools.
Frequently asked questions
Do QR codes expire?
Static QR codes do not expire on their own, because the destination is stored in the code itself. Dynamic codes can stop working if the redirect service is closed or unpaid.
Can a QR code be scanned if part of it is covered?
Often, yes — error correction lets a code survive small damage or a small central logo, but covering too much will break it. Always test after adding a logo.
Are QR codes safe to scan?
Usually, but check the address shown after scanning before entering passwords or payment details, and be wary of codes in unexpected messages or stickers placed over other codes.