QR Code Technical Guide
Everything you need to know about QR code technology: error correction, encoding modes, structure, and design best practices.
QR Code Structure
3 large squares at corners for detection and orientation
→ Lets scanners locate and orient the QR code
Smaller squares for version ≥2, helps with perspective correction
→ Corrects distortion from non-perpendicular scanning
Alternating black/white lines between finder patterns
→ Helps determine module size and grid alignment
Error correction level and mask pattern (15 bits × 2)
→ Tells scanner how to decode the data
Version number for QR codes version 7+ (18 bits × 2)
→ Indicates QR code size/version
The actual encoded content and Reed-Solomon error correction codes
→ Your data + ability to recover from damage
4-module white border around the entire code
→ Separates QR from surroundings for reliable detection
Error Correction Levels
QR codes use Reed-Solomon error correction. Higher levels = more redundancy = works even with damage, but holds less data.
| Level | Recovery | Best For |
|---|---|---|
| L | ~7% | Clean environments, maximum data capacity |
| M | ~15% | General purpose, balanced |
| Q | ~25% | Industrial, moderate damage expected |
| H | ~30% | Logos embedded, harsh conditions |
💡 Want to add a logo? Use Level H (30% error correction). Your logo can safely cover up to 30% of the QR code's data area.
Encoding Modes
QR codes optimize space by using different encoding modes based on content. Numeric mode is most efficient, byte mode is most flexible.
| Mode | Characters |
|---|---|
| Numeric | 0-9 |
| Alphanumeric | 0-9, A-Z, space, $%*+-./:) |
| Byte | Any (ISO 8859-1 / UTF-8) |
| Kanji | Japanese characters |
* Capacity shown is for Version 40 (largest) with Level L error correction
Size & Scanning Distance
Size Guidelines
- • Business cards: 15-20mm minimum
- • Posters: 2cm per meter of distance
- • Packaging: 20-30mm typical
- • Billboards: 25cm+ for highway scanning
Distance Formula
Distance ÷ 10 = Min QR SizeExample: Scan from 2 meters → QR should be at least 20cm
Design Best Practices
Size
- ✓ Minimum 2cm × 2cm for reliable scanning
- ✓ 1:10 ratio - scan distance : QR size
- ✓ Larger = scan from further away
Contrast
- ✓ Dark modules on light background (classic is best)
- ✓ Minimum 40% contrast difference
- ✓ Avoid: yellow on white, light gray modules
Quiet Zone
- ✓ Maintain 4-module white border minimum
- ✓ Don't crop or extend designs into quiet zone
- ✓ Background should not blend into QR edges
Error Correction
- ✓ Use Level H (30%) if adding logo
- ✓ Use Level M (15%) for general use
- ✓ Use Level L (7%) only when space is critical
Common Mistakes to Avoid
Inverting colors
Problem: White modules on dark background
Fix: Always use dark-on-light or test extensively before deploying
Low contrast
Problem: Blue on purple, gray on white
Fix: Ensure high contrast; when in doubt, use black on white
Damaged finder patterns
Problem: Logo covers corner squares
Fix: Only place logos in center, use H error correction
Too small
Problem: Low resolution printing, tiny screens
Fix: Test at actual size before production
No quiet zone
Problem: Design touches QR edge
Fix: Maintain 4-module white border
✅ Pre-Deployment Checklist
- ☐ Test with multiple phone brands (iPhone, Android)
- ☐ Test at intended scan distance
- ☐ Test in lighting conditions similar to deployment
- ☐ Verify destination URL/content is correct
- ☐ Check quiet zone is maintained
- ☐ Ensure good contrast (print a sample)
- ☐ Test after any compression (JPEG can ruin QR codes)
Create Perfect QR Codes!
Generate QR codes with customizable error correction, colors, and sizes.
📱Open QR Code Generator