Unicode in QR Codes

QR codes are everywhere — on product packaging, restaurant menus, business cards, and advertising. They were originally designed for tracking automotive parts in Japanese factories (by Denso Wave in 1994), but their ability to encode text has made them a universal data carrier. What many people do not realize is that QR codes can encode full Unicode text, enabling multilingual content, emoji, and characters from any writing system. This guide explains how Unicode works in QR codes, the encoding modes available, capacity trade-offs, and best practices for generating and scanning Unicode QR codes.

QR Code Encoding Modes

QR codes support four encoding modes, each optimized for different types of data:

Where does Unicode fit?

Unicode text is encoded using Byte mode — the QR code stores raw bytes, and the convention is to encode those bytes as UTF-8. This means any Unicode character can be stored in a QR code, but it consumes more capacity than ASCII-optimized modes.

The flow for Unicode text:

Unicode text ("Hello, world")
    |
    v
UTF-8 encoding (bytes)
    |
    v
QR code Byte mode (each byte = 8 bits in the QR symbol)
    |
    v
Scanner reads bytes
    |
    v
UTF-8 decoding -> Unicode text

The Kanji mode exception

Kanji mode is a special case for Japanese. It encodes Shift JIS double-byte characters at 13 bits per character, which is more efficient than Byte mode (16 bits for a two-byte Shift JIS character). However, Kanji mode is limited to the Shift JIS character set and cannot encode arbitrary Unicode. For modern multilingual use, Byte mode with UTF-8 is preferred.

Capacity and Unicode

QR code capacity depends on the version (size), error correction level, and encoding mode. Here is the maximum data capacity for the largest QR code (Version 40, 177x177 modules) at the lowest error correction (Level L):

UTF-8 byte cost per character

Since Unicode in QR codes uses Byte mode with UTF-8 encoding, the cost varies by script:

Practical capacity examples

For a Version 10 QR code (57x57 modules) with medium error correction (Level M):

Error correction levels

Higher error correction reduces data capacity. For Unicode-heavy QR codes where capacity is tight, Level L or M is recommended.

ECI (Extended Channel Interpretation)

The QR code specification includes ECI (Extended Channel Interpretation) — a mechanism to declare the encoding of Byte mode data:

The ECI problem

In theory, ECI 26 (UTF-8) should be included in any QR code containing UTF-8 data. In practice:

The industry has converged on an informal standard: Byte mode data is assumed to be UTF-8 unless an ECI indicator says otherwise. Most modern scanners (smartphone cameras, barcode scanner apps) handle UTF-8 correctly without an ECI declaration.

However, if you are encoding text for high-reliability applications (logistics, medical), including ECI 26 is a safer choice. Test with your target scanners.

Generating Unicode QR Codes

Python (qrcode library)

import qrcode

# UTF-8 is the default for string input
qr = qrcode.QRCode(
    version=None,  # Auto-size
    error_correction=qrcode.constants.ERROR_CORRECT_M,
    box_size=10,
    border=4,
)
qr.add_data("Unicode text here")
qr.make(fit=True)

img = qr.make_image(fill_color="black", back_color="white")
img.save("unicode_qr.png")

JavaScript (qrcode.js)

// Browser
const qr = new QRCode(document.getElementById("qrcode"), {
    text: "Unicode text here",
    width: 256,
    height: 256,
    correctLevel: QRCode.CorrectLevel.M
});

// Node.js (qrcode package)
const QRCode = require('qrcode');
QRCode.toFile('unicode_qr.png', 'Unicode text here');

Handling capacity overflow

If your Unicode text exceeds the capacity of a given QR version:

1. Increase QR version: Version 1 (21x21) to Version 40 (177x177)
2. Lower error correction: From H to M or L
3. Use a URL shortener: Encode a short URL that redirects to the full content
4. Compress the text: For structured data, use a compact format
5. Split across multiple QR codes: Some standards (e.g., Structured Append) allow linking multiple QR codes

Scanning and Decoding

How scanners handle Unicode

Modern QR code scanners (smartphone cameras, Google Lens, dedicated apps) typically:

1. Detect Byte mode data
2. Check for ECI indicator (if present, use declared encoding)
3. If no ECI, attempt UTF-8 decoding
4. If UTF-8 fails, fall back to ISO-8859-1 or system locale

Scanner compatibility for Unicode

Common scanning issues

Use Cases for Unicode QR Codes

Wi-Fi QR code with Unicode SSID

The Wi-Fi QR code format supports Unicode SSIDs:

WIFI:T:WPA;S:MyNetwork;P:password123;;

If the SSID contains Unicode characters, they are encoded as UTF-8 bytes in Byte mode. Most smartphone Wi-Fi QR scanners handle this correctly.

Key Takeaways

• QR codes store Unicode text via Byte mode with UTF-8 encoding. Any Unicode character — CJK, Arabic, emoji, and more — can be encoded in a QR code.
• Capacity decreases with character complexity: ASCII uses 1 byte per character, CJK uses 3, and emoji use 4. Plan your QR version and error correction level accordingly.
• ECI indicators formally declare UTF-8 encoding but are optional in practice. Most modern scanners assume UTF-8 by default.
• For maximum compatibility, keep QR content short, use error correction level M, and test with multiple scanners (iOS, Android, dedicated apps).
• When Unicode content exceeds QR capacity, use a URL shortener to redirect to the full content rather than trying to encode everything directly.