A4 ↔ Letter Paper Size Converter
Compare and convert between A4 (ISO) and Letter (US) paper sizes
A4 Paper
210 × 297 mm
8.27 × 11.69 in
ISO Standard (International)
Letter Paper
215.9 × 279.4 mm
8.5 × 11 in
US Standard
Size Comparison
A4 is 6% taller, Letter is 3% wider
Width Difference
+5.9 mm
Letter is wider
Height Difference
-17.6 mm
A4 is taller
Area Difference
-6.4%
A4 has less area
Aspect Ratio
1.41 vs 1.29
A4 is more square
📐 Visual Size Comparison
LETTER
A4
Blue: Letter Paper (US) | Green: A4 Paper (ISO)
📚 A4 vs Letter Paper: Key Differences
A4 Paper (ISO 216)
- Standard size: 210 × 297 mm
- Used in most countries worldwide
- Aspect ratio: 1:√2 (≈1.414)
- Part of ISO 216 standard
- When folded in half: A5 size
Letter Paper (US)
- Standard size: 8.5 × 11 inches
- Used in USA, Canada, Mexico
- Aspect ratio: 1.294:1
- Traditional US paper size
- Close to A4 but not identical
Geometric Comparison
A4: 210 × 297 mm (1:√2 ratio)
Letter: 215.9 × 279.4 mm
Letter is 5.9 mm wider (2.8%)
A4 is 17.6 mm taller (6.3%)
A4 area: 62,370 mm²
Letter area: 60,290 mm²
Letter: 215.9 × 279.4 mm
Letter is 5.9 mm wider (2.8%)
A4 is 17.6 mm taller (6.3%)
A4 area: 62,370 mm²
Letter area: 60,290 mm²
Practical Implications
- Printing: May require scaling
- Documents: Margins may shift
- Scanning: Automatic detection
- International business: Be aware
📏 Conversion Formulas
// Millimeters to Inches
inches = millimeters ÷ 25.4
// Inches to Millimeters
millimeters = inches × 25.4
// Standard Sizes
A4: 210 mm × 297 mm
= 8.27 in × 11.69 in
Letter: 8.5 in × 11 in
= 215.9 mm × 279.4 mm
inches = millimeters ÷ 25.4
// Inches to Millimeters
millimeters = inches × 25.4
// Standard Sizes
A4: 210 mm × 297 mm
= 8.27 in × 11.69 in
Letter: 8.5 in × 11 in
= 215.9 mm × 279.4 mm
📊 Quick Comparison Table
| Metric | A4 Paper | Letter Paper | Difference |
|---|---|---|---|
| Width (mm) | 210 mm | 215.9 mm | +5.9 mm |
| Height (mm) | 297 mm | 279.4 mm | -17.6 mm |
| Width (inches) | 8.27 in | 8.5 in | +0.23 in |
| Height (inches) | 11.69 in | 11 in | -0.69 in |
| Area | 62,370 mm² | 60,290 mm² | -2,080 mm² |
| Aspect Ratio | 1:1.414 (√2) | 1:1.294 | A4 is more square |
❓ Frequently Asked Questions
Q: Can I print A4 documents on Letter paper?
A: Yes, but you may need to scale the document. A4 is taller and narrower than Letter. Most printers can automatically scale to fit.
Q: Which countries use A4 vs Letter?
A: A4 is used in most countries worldwide (Europe, Asia, Australia, Africa). Letter is used primarily in the USA, Canada, and Mexico.
Q: Is A4 the same as Legal size?
A: No, Legal size (8.5 × 14 inches) is different from both A4 and Letter. A4 is between Letter and Legal in height.
Q: Why does A4 use the √2 aspect ratio?
A: The √2 (1:1.414) aspect ratio allows folding in half while maintaining the same proportions. This is why A4 folded becomes A5.