QR Code Generator — URLs, Text, WiFi, Email

How QR Codes Work

A QR code is a two-dimensional matrix symbology that encodes data as a grid of black and white squares called modules. The pattern is read by a camera, which locates the three large finder squares in the corners, decodes the version and format info, and then walks the data region extracting bits that are mapped back to the original text or bytes. The complete specification is published as ISO/IEC 18004:2015, and Denso Wave, the inventor, keeps the basic patent royalty-free, which is why QR codes spread so widely. A QR code symbol ranges in size from Version 1 (21 by 21 modules, up to 25 alphanumeric characters) to Version 40 (177 by 177 modules, up to 4,296 alphanumeric characters). Every symbol includes position-detection patterns, timing patterns, format information, and Reed-Solomon error correction so it can survive partial damage. For other tools in this category see our UUID generator and password generator.

The QR Encoding Process

Encoding a QR code follows six well-defined steps per ISO/IEC 18004. First, the encoder selects a mode (numeric, alphanumeric, byte, or Kanji) based on the character set in the input, because each mode packs bits differently; numeric mode uses 3.33 bits per digit, while byte mode uses 8 bits per character. Second, the encoder picks the smallest version that can hold the data at the chosen error correction level. Third, the data is converted to a bit stream, prefixed with a mode indicator and character count, and padded to the exact capacity. Fourth, Reed-Solomon error correction codewords are calculated and appended. Fifth, data and EC codewords are interleaved and placed on the module grid following a fixed walking pattern that skips the finder, alignment, and timing patterns. Sixth, one of eight masking patterns is applied to minimize long runs of the same color, and the format information is written. A worked example: the URL https://example.com is 19 bytes, which fits in a Version 2 symbol (25x25) at error correction level M.

Key Terms You Should Know

Module: a single black or white square, the smallest unit of a QR code. Version: a number from 1 to 40 that determines the grid size in modules; each version adds 4 modules on each side. Error correction level: L, M, Q, or H, indicating how much of the symbol can be damaged before it stops decoding. Finder pattern: the three concentric square markers in the top-left, top-right, and bottom-left corners that scanners use to locate and orient the code. Alignment pattern: smaller concentric squares added on Version 2 and above to correct for perspective distortion. Mask pattern: one of eight XOR patterns applied to the data bits to avoid confusing scanners with large solid areas. Quiet zone: the four-module-wide white border required around the symbol so scanners can separate it from the background.

QR Code Capacity by Version — Reference Data

Different versions of QR codes store very different amounts of data. The table below shows the alphanumeric and byte capacities for several common versions at error correction level M, as specified in ISO/IEC 18004 Annex E. Note how the capacity scales roughly quadratically with version number, but so does the printed size, so short text is better served by a small version. When generating a QR code for a printed flyer, most designers pick a version under 10 (57x57 modules) so the code remains easy to scan at normal distances. Version 40, the maximum, is rarely used because it requires a resolution-intensive image and a longer scan time.

Practical Examples

Example 1 — Restaurant menu: A cafe prints a QR code on every table that points to https://cafe.example/menu.pdf. Even with error correction level M, this 32-byte URL fits in a Version 3 symbol (29x29), which scans reliably from 60 cm away at a printed size of 25 mm. Example 2 — WiFi sharing: A hotel generates a WiFi QR code for its guest network. The encoded text is WIFI:T:WPA;S:Hotel_Guest;P:Welcome2024;;, which is 32 characters and fits in a Version 2 symbol. Guests scan the printed card, and their phone offers a one-tap connect button. Example 3 — Event ticket: A conference issues QR code tickets with a 36-character UUID as the ticket ID. The scanner at the door reads the ID in under 200 ms and checks it against the registration database, which handles 1,200 check-ins per hour per lane according to Eventbrite's 2023 operations data.

Tips and Best Practices

Keep URLs short: a shorter URL produces a smaller version, which is easier to scan and faster to decode; use a URL shortener or a branded redirect if possible. Test on multiple phones: iOS and Android handle low contrast and small sizes differently, so scan the printed output on both platforms before going to production. Maintain the quiet zone: always leave at least four modules of white space around the code; placing the symbol flush against a border is the number-one cause of scan failures. Raise the error correction level for printed media: ink bleed, smudging, and paper folds damage QR codes, so print at level Q or H. Pick dark on light: QR scanners expect dark modules on a lighter background; inverted codes fail on older scanner apps. Avoid tiny logos over finder patterns: the three corner markers must remain completely visible or decoding will fail. Print at 1 mm per module minimum: scanners need at least 2 camera pixels per module, so a 25x25 Version 2 symbol should be at least 25 mm across for reliable scanning from a phone at arm's length.