QR Codes & Barcodes Explained

A QR code (Quick Response code) is a two-dimensional (2D) matrix barcode: a square grid of black and white cells that encodes data in both the horizontal and vertical directions. Invented by Denso Wave in 1994 and standardised as ISO/IEC 18004, QR codes can store far more than a traditional 1D barcode and can still be read even when partly dirty or damaged. Today they appear on payments, tickets, packaging, WiFi sign-in cards, business cards and app-download links.

How a QR code stores data

The individual black and white cells are called modules. Data is encoded as a bit stream — each byte becomes a pattern of dark (1) and light (0) modules — then arranged into the grid following a fixed placement algorithm.

Several structural features let a scanner locate and decode the grid regardless of angle or orientation:

• Finder patterns — the three large concentric squares in the top-left, top-right and bottom-left corners. They let a scanner detect the code and work out its rotation.
• Alignment patterns — smaller squares (in larger versions) that correct for perspective distortion when the code is photographed at an angle.
• Timing patterns — alternating dark/light lines running between finder patterns that define the module coordinate grid.
• Quiet zone — a blank margin of at least 4 modules around the whole code. Without it, scanners struggle to isolate the code from surrounding content.
• Format & version information — encode the error-correction level and mask pattern, and (for larger codes) the version number.

Versions

QR codes come in 40 versions, from version 1 (21×21 modules) to version 40 (177×177 modules). Each step up adds 4 modules per side and stores more data. The generator picks the smallest version that fits your payload at the chosen error-correction level.

Error correction levels

QR codes use Reed–Solomon error correction, so a code stays readable even when part of it is obscured or damaged. There are four levels, trading data capacity for robustness — a higher level adds redundant data, meaning fewer usable modules and therefore a denser or larger code for the same payload.

Level	Approx. recovery	Trade-off	Typical use
L (Low)	~7%	Most data capacity, least robust	Clean on-screen display, short-lived codes
M (Medium)	~15%	Balanced default	General print and web use
Q (Quartile)	~25%	Denser, more robust	Codes exposed to dirt or wear
H (High)	~30%	Least capacity, most robust	Codes with a centre logo, industrial/outdoor use

If you place a logo in the middle of a code, use level H so the covered modules can be reconstructed.

Common QR payload formats

A QR code just stores text — but scanners recognise certain conventional string formats and act on them. The exact syntax matters; a stray character can stop a phone from offering the right action.

URL — the most common payload. Just the full address:

https://codingsetu.com/tools/qr

WiFi — join a network. Escape any ; , : \ in the SSID/password with a backslash:

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

T is the auth type (WPA, WEP, or nopass), S the SSID, P the password. For a hidden network append H:true;.

vCard / MeCard — a contact. MeCard is more compact:

MECARD:N:Doe,John;TEL:+911234567890;EMAIL:john@example.com;;

BEGIN:VCARD
VERSION:3.0
N:Doe;John
TEL:+911234567890
EMAIL:john@example.com
END:VCARD

Email, SMS, phone, location:

mailto:hello@example.com?subject=Hi&body=Message
SMSTO:+911234567890:Your message here
tel:+911234567890
geo:19.0760,72.8777

otpauth:// (TOTP) — provision a two-factor authenticator app. Defined by the Key URI format:

otpauth://totp/Example:alice@example.com?secret=JBSWY3DPEHPK3PXP&issuer=Example&algorithm=SHA1&digits=6&period=30

WhatsApp — open a chat via wa.me (number in international format, no + or spaces):

https://wa.me/911234567890?text=Hello

SEPA / EPC (Girocode) — a European bank transfer. The EPC QR standard uses a fixed line order:

BCD
002
1
SCT
BANKBEBBXXX
Jane Doe
BE72000000001616
EUR12.50

Invoice 123

1D vs 2D barcodes

A 1D (linear) barcode — EAN-13, UPC, Code 128, Code 39 — encodes data in the varying widths of vertical bars, read along a single line. It holds only a small amount of data (typically a product number) and has no error correction, but it is compact and universally supported at retail.

A 2D barcode stores data in a grid, packing much more information into a smaller area and adding error correction. The main 2D symbologies:

Symbology	Strengths	Typical use
QR code	High capacity, ubiquitous phone support, error correction	Marketing, payments, WiFi, tickets, GS1 Digital Link
Data Matrix	Very high density at tiny sizes; needs only 20% quiet zone	Direct part marking on small components, electronics, pharma (GS1)
Aztec	No quiet zone needed; central finder; robust on low-quality print	Transit and airline boarding passes / e-tickets

Data Matrix wins where space is extremely tight (marking a circuit board or surgical instrument). Aztec is common on rail and airline tickets because it needs no surrounding quiet zone and reads well from a phone screen or crumpled printout. QR dominates consumer-facing uses thanks to camera support on every phone. All three are increasingly used to carry GS1 structured data — see GS1 Digital Link, which lets a single QR act as both a product barcode and a web link.

Practical tips

• Keep URLs short. Fewer characters mean a lower version and larger, more scannable modules. Use a short domain or a link shortener rather than a long tracking URL.
• Raise the error-correction level for print and logos. Use Q or H for anything physical, especially if a logo overlaps the centre.
• Preserve the quiet zone. Leave at least 4 modules of blank margin on all sides — don’t crowd the code with text or graphics.
• Maximise contrast. Dark code on a light background works best. Avoid inverting colours (light on dark) and avoid low-contrast colour pairs; keep the finder patterns solid.
• Mind the size. A rough rule of thumb: scanning distance ÷ 10 gives the minimum code width (e.g. 1 m distance → ~10 cm code).
• Always test before printing. Scan the final artwork with several phones and camera apps, and re-test after the code is printed at real size.

Standards & references

• ISO/IEC 18004 — the QR code symbology specification (structure, versions, error correction, encoding).
• WiFi QR format — the WIFI: payload syntax as documented by the ZXing project.
• otpauth:// Key URI format — the TOTP/HOTP provisioning URI.
• GS1 Digital Link — encoding GS1 identifiers in a web-friendly QR.

Try it

Generate QR codes and barcodes for any of the formats above — entirely in your browser, with nothing uploaded — using the CodingSetu QR & barcode tools linked below.