How Much Data Can a QR Code Hold? - Inside Those Black-and-White Squares
Paying at a convenience store, boarding a train, adding a friend on LINE. You use QR codes every day, but do you know how much data fits inside those tiny black-and-white squares? The answer: up to about 1,800 kanji characters. That is roughly 4.5 pages of Japanese manuscript paper packed into one small square.
Data Capacity of a QR Code
| Data Type | Maximum Capacity | Everyday Comparison |
|---|---|---|
| Numbers only | 7,089 digits | About 640 phone numbers |
| Alphanumeric | 4,296 characters | About 30 X (formerly Twitter) posts |
| Binary (8-bit) | 2,953 bytes | About 3 KB of data |
| Kanji (Shift_JIS) | 1,817 characters | About 4.5 manuscript pages |
Numbers-only mode fits 7,089 digits, but kanji drops to 1,817 characters. As explained in Characters vs. Bytes, kanji takes more bytes per character, so fewer characters fit in the same space.
QR Code Versions and Sizes
QR codes have "versions." Higher versions store more data.
| Version | Module Grid | Max Digits (Numbers) | Common Use |
|---|---|---|---|
| 1 (smallest) | 21 x 21 | 41 | Short URLs |
| 5 | 37 x 37 | 154 | Typical URLs |
| 10 | 57 x 57 | 652 | Business card contact info |
| 20 | 97 x 97 | 2,061 | Long text |
| 40 (largest) | 177 x 177 | 7,089 | Bulk data (rarely used) |
Version 40 is made up of 177 x 177 = 31,329 black-and-white modules. In practice, almost nobody uses version 40. The more data you pack in, the bigger and more complex the code becomes, making it harder for phone cameras to scan.
What Everyday QR Codes Actually Contain
| Use Case | Data Inside | Approximate Size |
|---|---|---|
| LINE friend request | LINE URL (about 40 characters) | About 40 bytes |
| PayPay / QR payment | Payment URL + token | About 100-200 bytes |
| Website URL | URL string | About 30-100 bytes |
| Wi-Fi login | SSID + password + encryption type | About 50-150 bytes |
| Business card (vCard) | Name, phone, email, address | About 200-500 bytes |
| Airline boarding pass | Flight number, seat, passenger info | About 100-300 bytes |
Most QR codes you scan every day use less than 10% of the maximum capacity. A LINE friend request is about 40 bytes - just 1.4% of the 2,953-byte limit.
Error Correction in QR Codes
One of the coolest features of QR codes is that they still work even when part of the image is dirty or covered.
| Error Correction Level | Recoverable Damage | Effect on Capacity | Best For |
|---|---|---|---|
| L (Low) | About 7% | Maximum capacity | Clean environments (screens) |
| M (Medium) | About 15% | Slightly reduced | General printed materials |
| Q (Quartile) | About 25% | Noticeably reduced | Dirty environments |
| H (High) | About 30% | Minimum capacity | QR codes with logos |
At level H, a QR code still scans even if 30% of it is hidden. That is why companies can place their logo right in the center of a QR code. The trade-off is that stronger error correction means less room for data.
QR Codes vs. Barcodes
| Feature | Barcode (1D) | QR Code (2D) |
|---|---|---|
| Data capacity | About 20 digits max | Up to 7,089 digits |
| Data direction | Horizontal only | Both horizontal and vertical |
| Scan angle | Front only | 360 degrees, any angle |
| Error correction | None | Yes (up to 30%) |
| Japanese support | No | Yes |
A barcode holds about 20 digits at most - just enough for a product ID like a 13-digit JAN code. A QR code stores 350 times more data and supports Japanese characters. When Denso Wave (a Japanese company) invented the QR code in 1994, handling kanji was a key design goal.
QR Code Security Risks
| Risk | How It Works | How to Stay Safe |
|---|---|---|
| Fake QR codes | A sticker placed over the real code | Watch for suspicious stickers |
| Phishing | Code links to a fake website | Check the URL after scanning |
| Malware | Code links to a malicious app download | Do not scan unknown QR codes carelessly |
QR codes are convenient, but their weakness is that you cannot see what is inside before scanning. A written URL lets you spot a suspicious site, but a QR code hides it until you scan. Just like password length and security, balancing convenience and safety matters.
Books about QR codes and information technology are available on Amazon as well.