ISO 216 vs. North American Standards
Most of the world uses the ISO 216 standard (A4, A3, etc.). North America uses its own system (Letter, Legal, Ledger).
The A4 Standard (The Magic Ratio)
A-series paper is based on the aspect ratio of √2. This means if you fold an A4 in half, you get an A5 with the exact same proportions.
Comparison
- A4: 210 x 297 mm (8.3" x 11.7")
- Letter: 215.9 x 279.4 mm (8.5" x 11")
Key Takeaways
- A4 is taller and narrower than Letter
- Use A4 for international correspondence
- Most modern printers can handle both if configured correctly