QR Codes That Actually Scan: Size, Contrast, Error Correction and Content Choices

A QR code is a grid of dark and light squares called modules. More data means more modules, so each module has to be smaller for the same printed size. Scanners must be able to distinguish every module, so the practical limit is set by how large each one appears to the camera. That is why a short URL makes a more reliable code than a long one with tracking parameters.

• ▸A common rule: the code should be about one tenth of the scanning distance. A code scanned from 30 centimeters needs about 3 centimeters, and a poster scanned from 3 meters needs about 30.
• ▸For business cards and packaging, 2 by 2 centimeters is a practical minimum for a short link.
• ▸Printing resolution matters. Use vector formats such as SVG for print, which stay sharp at any size, and a high resolution PNG otherwise.
• ▸Avoid scaling a small bitmap up. Blurred module edges cause scanning failures.

• ▸Use dark modules on a light background. Black on white is the most reliable.
• ▸Colored codes are fine if the contrast is strong. Dark blue or dark green on white works, while light colors or a low contrast pair fail.
• ▸Inverted codes, with light modules on a dark background, are not supported by every scanner. Test before relying on one.
• ▸Do not place the code over a busy photograph or a gradient. Put it on a plain panel.
• ▸Glossy surfaces create glare. Choose a matte finish for codes on packaging.

The specification asks for a blank margin of four modules on every side. Without it, scanners cannot tell where the code begins. If you place text, a border or a graphic too close, scans fail. The margin setting in the QR Code Generator on this site is adjustable. For print, set it to at least four modules.

Error correction adds redundancy so that a scratched, dirty or partly covered code still reads. The four levels recover roughly 7, 15, 25 and 30 percent of the data. Higher levels make denser codes with smaller modules, so there is a trade-off.

• ▸Low: clean digital screens and very long data.
• ▸Medium: the default, good for most prints.
• ▸Quartile: outdoor prints and labels that may get scuffed.
• ▸High: required if you place a logo in the middle, since the logo covers part of the data. Keep the logo small, below about a fifth of the code's width.

• ▸A static code stores the data directly. It works forever and cannot be changed. A dynamic code points to a short redirect that you can edit later, but it depends on a service staying alive and may carry a cost.
• ▸Shorten the URL, or use a clean address that is easy to read in case the scan fails. Add the tracking parameters with the UTM Generator first.
• ▸Wi-Fi codes use a special format, so guests can join with one scan. Update the code when you change the password.
• ▸Phone, SMS and email codes open pre-filled actions, which are quick for people on a poster or a card.

• ▸Print a proof at the exact final size on the exact material.
• ▸Scan it with at least two different phones, one older, at the real distance and in the real light.
• ▸Test a few degrees of tilt and some shadow.
• ▸Open the destination on a mobile connection. A code that scans perfectly but opens a page that loads slowly or is not mobile friendly still fails.

Because people cannot read a code, they trust it. Attackers paste stickers over legitimate codes and send people to fake payment or login pages. If you publish codes in public places, check them periodically and make the destination address visible next to the code. As a user, look at the link your phone shows before opening it.