Question 1

What determines how much data a QR code can hold?

Accepted Answer

QR code capacity depends on two factors: version (1–40, where higher versions are larger grids with more modules) and error correction level (L/M/Q/H). Version 1 at L-level holds 41 alphanumeric characters. Version 40 at L-level holds up to 4296 alphanumeric or 7089 numeric characters. Adding a logo or increasing error correction reduces effective capacity. For URLs, keep content under 100 characters for best scanner compatibility.

Question 2

What are the four error correction levels and which should I use?

Accepted Answer

L (Low, ~7% recovery), M (Medium, ~15%), Q (Quartile, ~25%), H (High, ~30%). Higher levels create denser, more complex codes. Use L or M for clean digital displays and simple URLs. Use Q or H when the QR code will be printed on surfaces that may be worn, dirty, or partially obscured — and when embedding a logo (which intentionally damages part of the code).

Question 3

Why won't my QR code scan on some devices?

Accepted Answer

Common reasons: low contrast (dark code on dark background), too much data causing a very dense code, the quiet zone (white border) is too small, the code is too small when printed, or the camera lens is blurry. Fix: ensure minimum 4-module quiet zone around all sides, print at least 2×2 cm, maintain high contrast (black on white is ideal), and use error correction level M or Q for printed codes.

Question 4

Can I use colored or logo QR codes safely?

Accepted Answer

Yes, with precautions. The foreground (dark modules) must have sufficient contrast against the background — aim for at least 3:1 contrast ratio. For logos: cover no more than 30% of the code area and use H-level error correction to compensate for the covered modules. Avoid placing the logo over the three finder patterns (corner squares) — those are critical for detection. Test extensively across multiple devices before deploying.

Question 5

What types of content can QR codes encode beyond URLs?

Accepted Answer

QR codes can encode: plain text, URLs (http/https), email (mailto:), phone numbers (tel:), SMS (smsto:), Wi-Fi credentials (WIFI:S:ssid;T:WPA;P:password;;), contact cards (vCard/MECARD format), calendar events (VCALENDAR), geographic coordinates (geo:lat,lng), and app deep links. For Wi-Fi QR codes, most modern phones (iOS 11+, Android 10+) can automatically join the network by scanning.

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