QR Code Error Correction Levels

The Four Levels

They are named L, M, Q and H, recovering roughly seven, fifteen, twenty-five and thirty per cent of the code respectively. The redundancy is not free: it is extra data, so the same content at level H produces a denser grid than at level L. Denser grids need more physical space or a better camera to read, which is the trade being made every time someone raises the level.

Why a Logo in the Middle Works

Covering the centre of a code destroys part of the data, and error correction is what reconstructs it. At level H a reasonably sized logo is recoverable. This is also why logo placement goes wrong: the three large squares in the corners are position markers, not data, and no amount of error correction survives covering one. A logo belongs in the middle and nowhere near a corner.

When to Raise It

Raise it when the code will live somewhere unkind: a card carried loose in a pocket, a sticker outdoors, a printed menu that will be handled wet, anything behind glossy lamination that scatters light. Leave it lower when the code must be printed small, because density and small print fight each other and density loses.

The Quiet Zone Matters More

Most codes that fail to scan do not fail from damage. They fail because something is crowding them. A QR code needs a clear margin around it, conventionally four modules wide, and designers routinely trim it to make a layout fit. No error correction level compensates for a missing quiet zone, because the scanner cannot find the edges of the code in the first place.

Frequently asked questions

Which error correction level should I use?

M is a sensible default. Use H if you are placing a logo in the centre or the code will be handled a lot, and L only when you need the sparsest possible code.

Can I put my logo anywhere on a QR code?

Only in the middle. The three large corner squares are position markers, and covering one stops the code being found at all.

Why does my code not scan even though it looks fine?

Most often the quiet zone has been trimmed. A QR code needs clear space around it, and without it a scanner cannot locate the code.

Keep reading

Related terms

QR CodeA QR code (Quick Response code) is a two-dimensional barcode, a square grid of dark and light modules, that stores text such as a web address and can be read by a phone camera. Unlike a traditional barcode it holds data in both directions and still scans when partly damaged or obscured.Static QR CodeA static QR code encodes its destination or data directly in the pattern, so the code can never be edited and no service is needed for it to work. Whatever was encoded on the day it was generated is what every scan returns, for as long as the code remains legible.QR Code ScanningQR code scanning is the act of pointing a phone camera at a QR code so the phone reads the pattern and acts on what it holds, usually by offering to open a web address. Modern iPhones and Android phones do this in the built-in camera app, with no separate scanner required.QR Code Business CardA QR code business card is a business card whose contact details are reached by scanning a printed QR code. The code can either encode the details directly, which fixes them permanently, or point at a contact page, which keeps them editable after printing.

Put this into practice with your own card

Put your details on one card page, share it by link or QR code, and change them whenever they change. The printed code keeps working. No credit card required to start.

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