QR Codes Explained: How They Work and How to Make Your Own

QR codes have quietly become one of the most common ways to move information from a screen into a phone. Menus, Wi-Fi networks, event tickets, payment links — all of it travels through those little black-and-white squares. Yet most people treat them as a magic box: point a camera, and something happens.

This guide breaks that magic open. By the end you’ll understand how a QR code stores data, why some codes are denser than others, and how to generate a QR code you can actually use — and how to read one that’s been shared with you.

What a QR code actually is

QR stands for Quick Response. It was invented in 1994 by Masahiro Hara’s team at Denso Wave, a Toyota subsidiary, to track car parts faster than traditional barcodes.

A QR code stores data in a two-dimensional grid of black and white squares called modules. Unlike a one-dimensional barcode, which only holds a thin strip of data, a QR code spreads information across the whole square — which is why a single code can hold hundreds of times more data, and why you can scan it from any angle.

The three large squares in the corners are called finder patterns. They let a camera lock onto the code and figure out its orientation, even if the phone is tilted or the code is upside down.

What QR codes can store

A QR code is just a container for text. What the text means is up to whoever made it. The most common things coded into a QR code are:

• A website URL — the most common use. Scan and open a page.
• Wi-Fi credentials — the phone reads the network name and password and offers to join.
• Plain text — a message, a serial number, a note.
• Contact details — a vCard with a name, email, and phone number.
• Location or SMS — a map pin or a prefilled text message.

This is why a QR generator usually lets you pick a type rather than just typing raw text — it packages your input into the format the phone expects.

Error correction: why codes survive damage

The clever part of QR codes is Reed–Solomon error correction. Every code carries a little redundant data, so a scanner can reconstruct the content even when part of the code is dirty, torn, or covered.

The redundancy has four levels:

• L — recovers ~7% of the data
• M — recovers ~15% (a good default)
• Q — recovers ~25%
• H — recovers ~30%

Higher levels mean a more dense, harder-to-scan code. If you print a QR code on a poster or a sticker, a higher level (Q or H) buys you a safety margin. If you’re generating a clean digital code for a screen, L or M is plenty. It’s also why brands can stamp a logo in the middle of a code — with enough non-damaged data around it, the logo doesn’t break scanning.

Generating a QR code: what matters

When you make your own QR code, a few choices decide whether it scans well:

1. Contrast. Dark modules on a light background scan best. Light-on-dark or low-contrast designs often fail. If you change colors, keep them close to black-on-white.
2. Size. A code needs to be big enough for the camera to resolve. 100–1000 pixels is typical; on a poster, the printed code should be at least a few centimeters across.
3. Error-correction level. Choose based on how the code will be used — digital uses can be light (M), physical or printed uses should be heavier (Q or H).
4. Content length. The more data, the denser the code. A short URL scans far more reliably than a paragraph of text.

A good generator previews the code live as you type, so you can see the density and adjust before you ever save it. You can then download it as a PNG (full quality) or SVG (scales infinitely for print).

Scanning a QR code you received

If someone sends you a QR code image — in a PDF, a slide deck, or a message — you don’t need to reach for your phone. Most browsers now scan codes directly, but on a computer the easiest path is to drop the image into a QR reader. A good reader does two things: it decodes the content and classifies it, so if the code contains a URL it offers to open the link, and if it contains a Wi-Fi network it shows those details.

One practical habit worth adopting: check where a QR code points before you open it. QR codes are convenient, and convenient links are also easy to abuse. A quick scan with a reader that shows you the full URL is a cheap defense against QR phishing.

Quick Reference

• QR = “Quick Response”: a two-dimensional grid of modules invented by Denso Wave in 1994, holding hundreds of times more data than a barcode.
• A QR code is a container for text — URL, Wi-Fi credentials, vCard, plain text — and denser content makes a denser code.
• Reed–Solomon error correction has four levels (L ~7%, M ~15%, Q ~25%, H ~30%): heavier for print and logos, lighter for clean on-screen codes.
• Scannability comes from contrast, size, and short content: dark-on-light, big enough for the camera, and as little data as you need.
• Check where a code points before you open it — reading with a tool that shows the full URL is cheap QR-phishing protection.

Getting started

If you want to create a QR code for a link, a message, a contact card, or your Wi-Fi, the QR Code Generator builds it right in your browser — no account, no upload, no watermarks. And if someone sends you a QR code as an image, the QR Code Reader decodes it, figures out what type it is, and gives you the right action button.