QR Code Generator

Error correction levels L, M, Q and H: how to choose

Every QR code carries redundant data so it can still be read when part of it is damaged, dirty or covered. The standard, ISO/IEC 18004, defines four levels, and the level you choose trades capacity for resilience. Denso Wave, the Japanese company that invented the QR code in 1994, publishes a plain-language guide to how error correction works.

Higher error correction makes the pattern denser for the same amount of data, because more of the grid is spent on redundancy. A URL that fits neatly at level L may need a larger, busier code at level H. The practical rule most printers follow: use M for a normal label, step up to Q or H when the code will be handled, abraded or partially covered, and drop to L only when the code is large and displayed on a clean digital screen.

What the QR 'version' number means

The tool reports a version number for every code it builds, and that number is the size of the grid. Version 1 is the smallest, at 21 by 21 modules; each version up adds four modules to each side, so version 2 is 25 by 25, version 10 is 57 by 57, and the largest defined version, 40, is 177 by 177. Denso Wave's technical overview covers the same structure.

Bigger versions hold more data, and the encoder picks the smallest version that fits your content at the error correction level you asked for. A short URL like https://lelifi.com/ encodes in a low version; a paragraph of text pushes into the teens or twenties. The full range runs from version 1 to version 40.

You do not normally need to care about the version, but it is worth knowing two things. First, a higher version means a denser grid, and a denser grid needs a bigger print size to stay scannable at a given distance. Second, if you paste something long, the encoder climbs through the versions looking for a fit; if even version 40 at level L cannot hold it, the content is too large for one symbol and has to be shortened or split.

How much data fits, and what to do when it doesn't

Capacity depends on both the version and the error correction level. Here are the practical maxima for a few representative versions at each level:

In practice a URL is 20 to 100 characters, so almost anything you would realistically encode fits with room to spare. If you paste something too long for the selected level, this generator automatically steps the error correction down, from H to Q to M to L, until the content fits, and tells you which level it used. If even level L at version 40 is not enough, the tool says so and you need to shorten the content or split it across two codes.

Quiet zone and minimum print size: the two rules people skip

Two placement details decide whether a printed QR code scans reliably, and both are easy to get wrong.

The quiet zone. Every QR code needs a margin of blank space around it, the standard calls for four modules of clear space on all four sides. A module is one square of the grid, so for a 25-module code the quiet zone is four squares wide. Put a code too close to the edge of a business card, or wrap a border right up against it, and many scanners will refuse to lock on. Leave the margin empty; do not fill it with a caption or a frame.

The minimum size. As a working rule, keep the printed code at least 2 centimeters (about 0.8 inches) square for something a phone scans from up close, and scale up from there. A widely used formula is that the print size in centimeters should be at least the scanning distance in meters divided by ten, so a code read from 3 meters needs to be about 30 cm across. When in doubt, print bigger and test with two different phones before you commit to a large print run.

Wi-Fi QR codes: the WIFI: format explained

You can put a network's details into a QR code so guests join without typing a password. The format is a small text string that phones recognize:

WIFI:T:WPA;S:NetworkName;P:Password;;

• T is the security type: WPA for modern networks, WEP for the old standard, or nopass for an open network.
• S is the network name (the SSID), exactly as it appears in the Wi-Fi list.
• P is the password. Omit it entirely for an open network.
• The string ends with a double semicolon, which is easy to forget and a common reason a code silently fails.

Scan the finished code and both iPhone and Android offer to join the network automatically. One caution worth stating plainly: anyone who scans the code can read the password in it. Print a Wi-Fi code only for a network you are happy to share, a guest network is ideal, your main home network is not. If a field contains a semicolon, backslash or comma, it has to be escaped with a backslash.

Why these codes never expire (static vs dynamic QR codes)

There are two kinds of QR code in the world, and only one of them can be deactivated.

A static QR code, which is what this generator produces, has your content encoded directly into the pattern. The image is entirely self-contained: there is no server, no short link and no account between the code and the destination. It works offline, it works if the company that made it goes out of business, and it works forever as long as the thing it points to still exists. Nothing about the code can be revoked.

A dynamic QR code instead encodes a short redirect URL, and the real destination lives on the provider's server. That lets you change where the code points after it is printed and count scans, genuinely useful for campaigns. But it also means the code stops working the moment you stop paying, the provider shuts down, or the redirect is disabled. Many free generators use dynamic codes so they can start charging you after a trial.

For a menu, a Wi-Fi card, a product label or anything printed in bulk, a static code is the safer choice. Use dynamic codes only when you need to retarget a printed code later.

Dark mode, inverted colors and scan reliability

QR scanners are built to expect dark modules on a light background, and the standard assumes that polarity. Most modern phone cameras also read the inverse, light modules on a dark background, but support is not universal, and older scanner apps and some embedded readers fail on inverted codes.

If you want a dark-mode QR code, treat it as a risk to test, not a default. Keep strong contrast between the two colors: dark navy on white scans well, mid-gray on light-gray does not, and low-contrast pastel combinations fail outright. The same contrast thinking that applies to text on a screen applies here, a scanner needs the two colors to be clearly different in luminance, not just in hue.

Two other reliability traps: a logo placed in the center of the code eats into the data area, so if you overlay one, use a high error correction level (H recovers up to about 30 percent) to leave headroom, and never cover the three large square finder patterns in the corners. And avoid glossy laminates that throw glare under the camera flash, matte printing reads more consistently.