QR Codes: How They Work and How to Print One That Scans
QR codes are everywhere: on menus, posters, parcels and business cards. They look complicated, but the idea is simple, and following a few rules means yours will scan first time on any phone.
What is inside a QR code?
A QR code is a picture of text. The black and white squares store characters, usually a web address, but it can also be plain text, a phone number or Wi-Fi details. When your phone camera reads the code, it turns the squares back into that text and offers to open the link.
QR codes were invented in 1994 by Denso Wave, a Japanese company, to track car parts in factories. “QR” stands for “quick response”, because they were designed to be read fast from any angle.
The three big squares and the quiet zone
The three large squares in the corners tell the scanner where the code is and which way up it is, so it can be read upside down or at an angle. The empty white border around the code, called the quiet zone, separates it from everything else. Cut it off or print the code on a busy background, and many phones will fail to find it.
Built-in damage repair
QR codes store backup information so they still work when part of the code is dirty, torn or covered. There are four repair levels:
| Level | Can recover | Good for |
|---|---|---|
| L (low) | about 7% | Clean screens and digital use |
| M (medium) | about 15% | Most printed codes (what t4io uses) |
| Q (quartile) | about 25% | Outdoor or industrial use |
| H (high) | about 30% | Codes with a logo placed on top |
Static or dynamic codes?
A static code stores your link directly in the squares. It works forever and nobody can switch it off, but you cannot change the link later.
A dynamic code stores a short link to a company’s server, which then forwards people to your page. You can change where it goes, and the company can count scans. But if you stop paying, or the company closes, every printed code stops working. For most people, static codes are the safer choice. All codes made on t4io are static.
Checklist before you print
- Scan it with at least two different phones.
- Open the link and check it goes to the right page, and that the page works on a phone.
- Make it big enough: about one tenth of the scanning distance.
- Keep dark squares on a light background, with a clear white border.
- Add a short label such as “Scan for the menu”, so people know what they will get.
Stay safe when scanning
Because a QR code hides its link, scammers sometimes stick fake codes over real ones on parking meters and posters. Before opening a link from a code in a public place, look at the address your phone shows. If it looks strange, or asks you to log in or pay, do not continue.