What a QR Code Is
A QR code, short for Quick Response code, is a two dimensional matrix bar code invented in 1994 by Masahiro Hara at the Japanese automotive supplier Denso Wave. It was designed to be scanned from any angle and to carry far more data than the one dimensional bar codes used in supermarkets. Since smartphone cameras added native QR support in the late 2010s, the format has spread from factory floors to restaurant menus, payment systems and public health check-ins.
QR codes can hold up to 7089 numeric digits, 4296 alphanumeric characters or 2953 bytes in the largest version 40 size with low error correction. In practice most QR codes encode a short URL of 20 to 60 characters, which fits comfortably in a small version 3 to 6 code that still scans at phone range.
How It Works
A QR code is built from a grid of modules (the little squares). Three large corner squares are called finder patterns and tell the scanner the orientation. Smaller alignment and timing patterns help cameras correct for perspective and distortion. The remaining data cells are grouped using Reed-Solomon error correction, which is how the code can still be read when up to 30 percent is damaged.
Four error correction levels are defined. Level L recovers up to 7 percent of damage, M 15 percent, Q 25 percent and H 30 percent. Higher levels add parity cells, which make the code denser for the same amount of content. If you plan to overlay a logo in the middle of the code, use Q or H so the scanner can rebuild the obscured region.
How to Use This Tool
- Type or paste your URL or text into the input box.
- Pick an output size in pixels: 200, 300, 400 or 600.
- Choose an error correction level. Use Medium unless you need a logo overlay.
- Click Generate QR to render the code.
- Scan with your phone to verify it opens the correct destination.
- Click Download PNG to save the image for print or embed.
Common Use Cases
- URL sharing: Point a phone at a code and open a web page without typing.
- Wi-Fi sharing: Encode the WIFI:T:WPA;S:MyNetwork;P:password; string so guests join without asking.
- vCard contacts: Share a business card as a scannable code that saves name, phone and email.
- Payments: Alipay, UPI, Paytm and many bank apps use QR for merchant payments.
- Product info: Print on packaging to link to manuals, recipes or recycling guidance.
- Menus and ordering: Restaurants pin a code to each table that opens the live menu.
Common Mistakes
- Low contrast colours. Dark modules must be clearly darker than light modules.
- Printing the code too small for the scanning distance. A 1 metre scan needs about a 10 cm code.
- Forgetting the quiet zone. Leave at least 4 modules of white space around the outside.
- Relying on URL shorteners that might expire, breaking the code permanently.
- Placing the code on a curved or reflective surface that distorts the pattern.
Static vs Dynamic QR Codes
A static QR code encodes the destination directly. Once printed it cannot be changed, but it also cannot be revoked if the owner forgets to renew a subscription. A dynamic QR code encodes a short redirect URL on a third party service, which forwards to the real destination. Dynamic codes let the owner update the target later and often provide scan analytics, but they rely on the redirect service staying online and often require a paid plan.
For permanent prints such as a plaque or a monument marker, prefer static. For a marketing campaign where the destination may change, dynamic makes sense, provided the service is from a reputable provider with a clear long term plan.
Privacy
This tool generates the QR code in your browser using a small open source JavaScript library. The content you enter is never uploaded, logged or tracked.
Frequently Asked Questions
What is the maximum amount of data a QR code can hold?
A QR code can hold up to 7089 numeric digits, 4296 alphanumeric characters, 2953 bytes or 1817 Kanji characters at the highest version 40 with low error correction. Practical limits are much smaller for reliable scanning.
What do the error correction levels mean?
L recovers 7 percent of damaged data, M recovers 15 percent, Q recovers 25 percent and H recovers 30 percent. Higher levels mean a denser code but better recovery from scratches or a logo overlay.
Can a QR code be hacked?
QR codes themselves are static data. The risk is the destination they point to. Attackers can replace a printed QR with a sticker pointing to a phishing site. Always verify the preview URL in your scanner before tapping.
What is the difference between static and dynamic QR codes?
Static QR codes encode the final destination directly. Dynamic QR codes encode a short redirect URL on a third party service, which lets the owner change the destination later or track scans but requires that service to remain online.
What size should I print a QR code?
The standard rule is the code should be at least 1 tenth the scanning distance. For a distance of 1 metre, print at 10 centimetres. For posters seen from across a room, go bigger.
Do QR codes expire?
Static QR codes do not expire. Dynamic QR codes rely on a redirect service and will break if that service shuts down or the subscription lapses. Prefer static for permanent prints.
Is the generator private?
Yes. The QR code is produced in your browser by a small open source library. Your content is not uploaded or logged.