QR Code

A QR code is a printable square barcode that any modern phone camera can read. Point your camera at the pattern of black-and-white squares, and your phone offers to open whatever the code points to — usually a web page. iOS and Android have built it into the default camera since 2017.

A restaurant prints a QR code on each table that opens its menu. A diner aims their phone, taps the notification, and the menu appears in the browser.

QR codes are a two-dimensional barcode — data is arranged across a grid, not just left-to-right like a supermarket barcode. That's where the bigger storage capacity comes from.

Anatomy

A QR code isn't a random pattern. It has specific regions a scanner reads before getting to the actual data.

Anatomy of a QR code

Finder pattern

Three nested squares in three corners. Lets a scanner orient the code at any angle.

Alignment pattern

A smaller nested square that helps scanners correct for perspective on curved or tilted surfaces.

Timing patterns

Alternating dark/light modules between the finder patterns. Tells the scanner how big each module is.

Format & version info

Encodes the error correction level and the QR version (size). Read first by the scanner.

Data & error correction

The actual encoded payload, plus Reed–Solomon parity bytes that let the code survive damage.

Quiet zone

The blank margin around the code. Required by the spec — at least 4 modules wide.

The grid above is illustrative — real QR codes have hundreds to thousands of modules. The structural regions are the same at every size.

The three big nested squares in the corners are the finder patterns. They're why QR codes can be scanned at any angle — they're the first thing the decoder locates, and the asymmetry (three corners, not four) tells the scanner which way is up.

How it actually encodes data

Every QR code has two key properties: a version (1 to 40, where version 1 is a 21×21 grid and version 40 is 177×177) and an error correction level (Low, Medium, Quartile, or High). Together they determine how much data fits.

Some squares aren't data — they're spare copies, used to recover the rest if part of the code is damaged or covered. The four error correction levels recover roughly 7%, 15%, 25%, and 30% of a damaged code respectively. Higher correction survives more damage but takes more squares.

The "QR" stands for Quick Response. Denso Wave (a Toyota subsidiary) invented the format in 1994 to track car parts on assembly lines, pitched as ten times faster to scan than the 1D barcodes it replaced.

Try it

Higher error correction makes the code more resilient but denser. Type something and watch the same payload render at all four levels.

Try it — error correction levels

53 chars encoded

LLow

~7% recoverable

Smallest module count. Use only when you fully control the print quality.

MMedium

~15% recoverable

The default for most generators. Reasonable balance of density and resilience.

QQuartile

~25% recoverable

Survives moderate damage. Recommended when adding a logo overlay.

HHigh

~30% recoverable

Densest. Use for outdoor, industrial, or branded codes with large logo overlays.

Higher error correction means the code can survive more damage — scratches, smudges, or a logo overlay — but uses more modules to encode the same payload. Pick the lowest level that survives your real-world print conditions.

Static vs dynamic QR codes

A static QR code encodes the destination URL directly. Once printed, you can't change where it points without printing a new code.

A dynamic QR code encodes a short URL instead. The QR code never changes; only the destination behind the short URL does.

Dynamic codes are the right default for anything you print — the QR can outlive the campaign that created it.

Common mistakes

Encoding a long URL directly. Every extra character pushes the QR to a bigger version with more squares — denser and harder to scan. Wrap it in a short URL first.
Skipping the blank margin. The 4-square-wide blank border (the quiet zone) is required for reliable scanning. Designs that crop or fill it scan inconsistently.
Logo overlay too large. A logo covering 25% of a Low-correction code will likely fail to decode. Bump to Quartile or High if you want a logo bigger than ~10%.
Low contrast or inverted colors. Dark squares on a light background is the standard. Light-on-dark works in some scanners and fails in others.
No print-quality test. A QR that scans cleanly on screen at 100% may not scan when printed at 1 inch on rough cardboard. Test the actual printed output from realistic distance.

QR codes also encode Wi-Fi, contact info, payments

URLs are by far the most common payload, but the format also supports Wi-Fi credentials, contact cards (vCard), email addresses, and geographic coordinates. Modern phone cameras recognize these formats and offer to act on them — joining the Wi-Fi, saving the contact, opening the map.

In China and parts of Southeast Asia, QR codes are also the dominant way to pay for things (WeChat Pay, Alipay) — driving a decade of investment in scanning UX that the rest of the world is now catching up with.

References

The QR code format is documented in ISO/IEC 18004. The basic specification is patent-free, which is why every phone can ship a built-in scanner.