A barcode is a machine-readable visual representation of data using a series of parallel lines (bars) of varying widths. The most common type is the 1D barcode — a single row of bars that encodes data horizontally. When a laser or camera scanner reads the barcode, it measures the widths of the bars and spaces to decode a number or short alphanumeric string.

Common Barcode Types

• UPC-A (Universal Product Code) — 12-digit numeric code used on retail products in North America. The standard on every grocery item since 1974.
• EAN-13 (European Article Number) — 13-digit international equivalent of UPC, used on products worldwide outside North America.
• Code 128 — Higher-density 1D barcode supporting all 128 ASCII characters. Common in logistics, shipping labels, and healthcare (medication tracking).
• Code 39 — Older alphanumeric barcode, still widely used in automotive and defense industries.
• QR Code (2D) — Technically a type of 2D barcode, though commonly treated as a separate category. Discussed in full below.
• PDF417 — Another 2D format used on driver's licenses and airline boarding passes.

The key limitation of 1D barcodes is data density. A standard UPC or EAN barcode stores only a product identifier number — the meaning of that number (price, name, stock level) is looked up in an external database. The barcode itself contains no product description, price, or other details. This works well for closed supply-chain systems but is limiting for consumer-facing applications.

Dedicated barcode scanners use laser technology optimized for fast, accurate 1D barcode reads on high-speed conveyor belts and checkout lanes. These scanners can read thousands of barcodes per minute — a speed advantage over camera-based QR scanning in high-volume warehouse contexts.

A QR code (Quick Response code) is a 2D matrix barcode invented by Denso Wave in Japan in 1994. Instead of a single row of bars, a QR code arranges data in a square grid of black and white modules (dots). This 2D layout allows far more data to be packed into the same physical space, and allows the code to be read from any direction.

How QR Codes Work

A QR code consists of several key structural elements:

• Position detection squares — the three large squares in the corners that allow the scanner to locate and orient the code instantly, regardless of angle or rotation
• Data modules — the black and white dots throughout the code body that encode the actual data
• Error correction blocks — redundant data blocks that allow the QR code to be read even when up to 30% of its area is damaged, dirty, or obscured by a logo
• Timing patterns — alternating black/white lines that help the scanner determine the size and density of the data grid

QR Code Data Types

A single QR code can encode any of the following data types:

• URL — the most common use; opens a website or landing page when scanned
• Plain text — a message, instructions, or description up to ~4,000 characters
• vCard contact — full contact card (name, phone, email, company) that saves directly to the scanner's contacts
• WiFi credentials — SSID and password that connects the scanner's device to a network automatically
• Phone number, SMS, or email — pre-fills an action for the user to complete
• Geographic coordinates — opens the location in a maps app
• Payment information — used in payment systems (WeChat Pay, Alipay, UPI in India)

Error Correction Levels

QR codes have four error correction levels: L (7%), M (15%), Q (25%), and H (30%). Higher error correction makes the code readable even when partially covered — essential for QR codes with logos embedded in the center. The trade-off is a more complex, denser code that requires more physical space to print reliably.