Paper Sizes: ISO vs ANSI, Printer Paper Size Guide
Paper sizes and printer paper size explained. Compare ISO (A4, A3) and ANSI (Letter, Legal). Paper size chart for printing and documents.
Paper size standards vary around the world, with two major systems dominating: ISO (International Organization for Standardization) and ANSI (American National Standards Institute). Understanding these standards helps you choose the right paper size for your needs and ensures compatibility with international documents.
ISO 216 Standard
The ISO 216 standard defines the A-series of paper sizes, which is used in most countries outside of North America. The standard is based on a mathematical ratio (√2:1), meaning that when you cut a sheet in half, you get two sheets with the same aspect ratio.
Common ISO Sizes
- A4: 210 × 297 mm (8.27 × 11.69 inches) – Most common size worldwide
- A3: 297 × 420 mm (11.69 × 16.54 inches) – Double the size of A4
- A5: 148 × 210 mm (5.83 × 8.27 inches) – Half the size of A4
- A6: 105 × 148 mm (4.13 × 5.83 inches) – Postcard size
ANSI Standard
The ANSI standard is primarily used in the United States and Canada. Unlike ISO sizes, ANSI sizes don't follow a consistent mathematical ratio, but they have become deeply ingrained in North American business and academic practices.
Common ANSI Sizes
- Letter: 8.5 × 11 inches (216 × 279 mm) – Standard US business and academic size
- Legal: 8.5 × 14 inches (216 × 356 mm) – Used for legal documents
- Tabloid: 11 × 17 inches (279 × 432 mm) – Also known as Ledger
Key Differences
Aspect Ratio
ISO A-series papers maintain a consistent √2:1 aspect ratio across all sizes, making scaling and folding more intuitive. ANSI sizes have varying aspect ratios, which can make scaling less straightforward.
Geographic Usage
ISO sizes are used in most of the world, including Europe, Asia, Africa, and South America. ANSI sizes are primarily used in North America. This geographic difference is important to consider when creating documents for international audiences.
Size Comparison
A4 (210 × 297 mm) is slightly narrower and taller than US Letter (216 × 279 mm). While the difference is small, it can cause formatting issues when printing documents designed for one standard on paper from the other standard.
When to Use Each Standard
Use ISO (A4) When:
- Creating documents for international audiences
- Working in countries outside North America
- You need consistent scaling (A3 folds to A4, A4 folds to A5, etc.)
- Designing for digital distribution (A4 is the default in most PDF viewers worldwide)
Use ANSI (Letter) When:
- Creating documents for North American audiences
- Printing in the United States or Canada
- Working with US-based businesses or educational institutions
- Creating legal documents (Legal size is 8.5 × 14 inches)
Digital Considerations
When creating digital documents, especially PDFs, it's important to specify the correct paper size. The PDF specification supports both ISO and ANSI sizes, and most PDF readers can handle either format. However, for best results, use the standard expected by your target audience.
Conclusion
Both ISO and ANSI standards serve their purposes and are well-established in their respective regions. The choice between them depends on your geographic location, target audience, and specific use case. For international work, ISO A4 is generally the safer choice, while North American audiences typically expect Letter size. Understanding these standards helps ensure your documents are properly formatted and compatible with your intended use.