A Link Someone Can Reach Without Typing
QR codes solve a narrow problem well: getting a piece of data from a physical surface into a phone without anyone transcribing it. A menu, a poster, a parcel label, a conference badge, anywhere a URL would be tedious and error-prone to type, a code removes the typing entirely.
This generator builds codes for links, plain text, contact details and Wi-Fi credentials, and produces them at a size and error correction level you choose.
How to Generate a QR Code
The content type matters, because a code that encodes structured data does more than one that encodes a bare string.
- Choose what the code should contain, a URL, plain text, contact details or Wi-Fi credentials.
- Enter the data. Keep URLs as short as you reasonably can, since more characters means a denser code that is harder to scan.
- Pick an error correction level. Medium is the usual default; go higher only if the code will carry a logo or be printed somewhere it may get damaged.
- Set the size. For print, larger is safer, a code needs roughly a centimetre of width for every ten centimetres of scanning distance.
- Download the image and test it with an actual phone before printing anything in quantity.
- Leave the quiet zone intact. The white border around a code is part of the specification, and cropping it is the most common reason a printed code will not scan.
Error Correction and Why It Matters
QR codes carry redundant data using Reed-Solomon coding, so a damaged or partly obscured code can still be read. Four levels are defined, recovering roughly 7, 15, 25 and 30 per cent of the code. The cost is density: higher correction means more modules for the same content, which makes the code visually busier and harder to scan at a distance or at small print sizes.
The practical use of high correction is placing a logo in the centre. That deliberately destroys part of the code, and level H tolerates it. For an undamaged code on a screen or a clean printed surface, level M is sufficient and scans more readily, so raising the level "just in case" usually makes things worse rather than better.
Error Correction Levels
What each level recovers and where it earns the extra density.
| Level | Recovery | Density cost | Use when |
|---|---|---|---|
| L (Low) | ~7% | Smallest code | Clean screens, very long data |
| M (Medium) | ~15% | Slight | The general default |
| Q (Quartile) | ~25% | Noticeable | Industrial or outdoor surfaces |
| H (High) | ~30% | Largest code | A logo overlaid on the centre |
Capacity moves in the opposite direction. At level L a code holds up to about 4,296 alphanumeric characters; at level H that falls to roughly 1,852. A long URL at level H can push the code into a density that scans poorly.
Printing, Contrast and Testing
Contrast is what scanners rely on, and inverting a code, light modules on a dark background, breaks many readers even though the pattern is intact. Dark on light is the specification. Coloured codes work if the contrast ratio stays high, but a mid-tone on a mid-tone will fail regardless of how well the design reads to a human eye.
Always test the actual printed artefact rather than the file. A code that scans on screen can fail on paper because of ink spread, a glossy finish reflecting light, or a curved surface such as a bottle. Testing with two or three different phones catches most problems, since camera and decoder quality vary considerably.