Paper Size Comparison
Compare all standard paper sizes from ISO A-series (international) and US/ANSI standards. Understand the key differences between A4 and Letter paper, and explore dimensions in inches, millimeters, and pixels.
Quick Comparison: A4 vs Letter
| Size | Standard | Dimensions (inches) | Dimensions (mm) | Pixels @ 300 DPI | Aspect Ratio |
|---|---|---|---|---|---|
| A4 | ISO 216 (International) | 8.27 × 11.69" | 210 × 297 mm | 2480 × 3508 px | 1:√2 (~1:1.414) |
| Letter | ANSI (US/Canada/Mexico) | 8.5 × 11" | 215.9 × 279.4 mm | 2550 × 3300 px | ~1:1.294 |
Key Difference: Letter paper is 6mm (0.24") wider but 18mm (0.71") shorter than A4. Letter is used primarily in North America, while A4 is the international standard used in most of the world.
ISO A-Series Sizes (International Standard)
The ISO 216 A-series is the international standard, used worldwide except in North America. All A-series sizes maintain a consistent √2 (1:1.414) aspect ratio, meaning each size is exactly half the previous one when folded.
| Size | Inches | Millimeters | Pixels @ 300 DPI | Common Uses |
|---|---|---|---|---|
| A0 | 33.11 × 46.81" | 841 × 1189 mm | 9933 × 14043 px | Posters, technical drawings |
| A1 | 23.39 × 33.11" | 594 × 841 mm | 7016 × 9933 px | Flip charts, posters |
| A2 | 16.54 × 23.39" | 420 × 594 mm | 4961 × 7016 px | Small posters, diagrams |
| A3 | 11.69 × 16.54" | 297 × 420 mm | 3508 × 4961 px | Presentations, drawings |
| A4 | 8.27 × 11.69" | 210 × 297 mm | 2480 × 3508 px | Documents, letters (most common) |
| A5 | 5.83 × 8.27" | 148 × 210 mm | 1748 × 2480 px | Notepads, flyers |
| A6 | 4.13 × 5.83" | 105 × 148 mm | 1240 × 1748 px | Postcards, invitations |
| A7 | 2.91 × 4.13" | 74 × 105 mm | 874 × 1240 px | Business cards (Europe) |
| A8 | 2.05 × 2.91" | 52 × 74 mm | 614 × 874 px | Tickets, labels |
| A9 | 1.46 × 2.05" | 37 × 52 mm | 437 × 614 px | Small labels, stamps |
| A10 | 1.02 × 1.46" | 26 × 37 mm | 307 × 437 px | Stamps, small labels |
Pro Tip: The √2 ratio means when you cut an A4 sheet in half along the long edge, you get exactly two A5 sheets with the same proportions. This scaling property works throughout the entire series: A0 → 2× A1 → 4× A2 → 8× A3, and so on.
US/ANSI Paper Sizes (North American Standard)
The ANSI standard is used primarily in the United States, Canada, Mexico, and parts of Latin America. Unlike ISO sizes, US paper sizes don't have a consistent aspect ratio.
| Size | ANSI Name | Inches | Millimeters | Pixels @ 300 DPI | Common Uses |
|---|---|---|---|---|---|
| Letter | ANSI A | 8.5 × 11" | 215.9 × 279.4 mm | 2550 × 3300 px | Documents, letters (most common) |
| Legal | — | 8.5 × 14" | 215.9 × 355.6 mm | 2550 × 4200 px | Legal documents, contracts |
| Tabloid | ANSI B | 11 × 17" | 279.4 × 431.8 mm | 3300 × 5100 px | Newspapers, posters, presentations |
| Ledger | ANSI B | 17 × 11" | 431.8 × 279.4 mm | 5100 × 3300 px | Spreadsheets, ledgers (landscape) |
| Executive | — | 7.25 × 10.5" | 184.2 × 266.7 mm | 2175 × 3150 px | Stationery, planners |
| ANSI C | ANSI C | 17 × 22" | 431.8 × 558.8 mm | 5100 × 6600 px | Architectural drawings |
| ANSI D | ANSI D | 22 × 34" | 558.8 × 863.6 mm | 6600 × 10200 px | Engineering drawings |
| ANSI E | ANSI E | 34 × 44" | 863.6 × 1117.6 mm | 10200 × 13200 px | Large architectural plans |
Note: Tabloid and Ledger are the same size (ANSI B) but in different orientations. Tabloid is portrait (11×17"), while Ledger is landscape (17×11").
Direct Size Comparisons
ISO vs US Equivalent Sizes
| ISO Size | Closest US Equivalent | Difference |
|---|---|---|
| A4 (210 × 297 mm) | Letter (215.9 × 279.4 mm) | Letter is 6mm wider, 18mm shorter |
| A3 (297 × 420 mm) | Tabloid (279.4 × 431.8 mm) | A3 is 18mm wider, 12mm shorter |
| A5 (148 × 210 mm) | Statement (139.7 × 215.9 mm) | A5 is 8mm wider, 6mm shorter |
| A2 (420 × 594 mm) | ANSI C (431.8 × 558.8 mm) | ANSI C is 12mm wider, 35mm shorter |
Visual Size Relationships
- A4 = 2 × A5 = 4 × A6 = 8 × A7 (exact halving)
- Letter ≠ 2 × Half Letter (Half Letter is 5.5×8.5", not proportional)
- Tabloid = 2 × Letter (side-by-side, but aspect ratio differs)
- A0 = 1 square meter (exactly 1 m² in area)
ISO B-Series Sizes (Less Common)
The ISO B-series is intermediate between A-series sizes, often used for books, passports, and envelopes. B-sizes are the geometric mean between consecutive A-sizes.
| Size | Inches | Millimeters | Pixels @ 300 DPI | Common Uses |
|---|---|---|---|---|
| B0 | 39.37 × 55.67" | 1000 × 1414 mm | 11811 × 16693 px | Large posters |
| B1 | 27.83 × 39.37" | 707 × 1000 mm | 8346 × 11811 px | Posters |
| B2 | 19.69 × 27.83" | 500 × 707 mm | 5906 × 8346 px | Posters |
| B3 | 13.90 × 19.69" | 353 × 500 mm | 4169 × 5906 px | Newspapers |
| B4 | 9.84 × 13.90" | 250 × 353 mm | 2953 × 4169 px | Books, newspapers |
| B5 | 6.93 × 9.84" | 176 × 250 mm | 2079 × 2953 px | Books, passports |
| B6 | 4.92 × 6.93" | 125 × 176 mm | 1476 × 2079 px | Pocket books |
B-Series Formula: B4 is the geometric mean between A3 and A4, meaning B4 = √(A3 × A4). This makes B-series useful for books that need to accommodate A-series content with margins.
Understanding the √2 Aspect Ratio
The √2 (1:1.414) aspect ratio used in ISO paper sizes has several practical advantages:
Why √2 is Ideal for Paper
- Perfect Scaling: When you fold an A4 sheet in half, you get exactly A5 with the same proportions
- No Waste: Two A4 pages fit perfectly on one A3 sheet without any wasted space
- Consistent Layouts: Documents maintain the same margins and proportions when scaled up or down
- Mathematical Elegance: √2 is the only aspect ratio where halving preserves the ratio
Proof of the √2 Property
For a rectangle with aspect ratio 1:√2:
- Original: 1 × √2
- When folded in half: √2/2 × 1 = 1/√2 × 1
- Flip it: 1 × √2 (same aspect ratio!)
Historical Note: The ISO 216 standard was introduced in 1975 but is based on a DIN standard from 1922 Germany. The √2 ratio was chosen specifically for its scaling properties, making it ideal for mass printing and photocopying.
Practical Printing Considerations
Bleed and Safe Zones
When printing professional documents, add bleed beyond the final trim size:
- Standard Bleed: 3mm (ISO) or 0.125" (US) beyond trim on all sides
- Safe Zone: Keep important content 3-5mm (ISO) or 0.125-0.25" (US) inside trim
- A4 with Bleed: 216 × 303 mm (instead of 210 × 297 mm)
- Letter with Bleed: 8.75 × 11.25" (instead of 8.5 × 11")
DPI Recommendations
- Office Documents: 150-200 DPI (draft quality)
- Professional Documents: 300 DPI (standard)
- High-Quality Print: 600 DPI (brochures, magazines)
- Large Format (Posters): 150 DPI (viewed from distance)
Cross-Border Compatibility
If you need to print documents in both US and international markets:
- Use margins of at least 0.75" (19mm) on all sides to ensure content fits on both Letter and A4
- A4 content fits on Letter when printed with reduced margins or scaled to 94%
- Letter content may be cut off on A4 if margins are too small
- Design for the smaller common area: 8.27 × 11" to be safe on both
Regional Paper Size Usage
Countries Using ISO A-Series (A4)
Most of the world uses ISO 216 (A4) as the standard, including:
- All of Europe
- All of Asia (except Philippines)
- All of Africa
- All of Oceania
- Most of South America
Countries Using US Letter Size
The US Letter size is primarily used in:
- United States
- Canada
- Mexico
- Parts of Central America (Guatemala, Costa Rica, Panama)
- Parts of South America (Colombia, Chile - partially)
- Philippines
Travel Tip: If you're traveling internationally with documents to print, use A4 format or ensure your printer supports both standards. Most modern printers support both, but availability of paper sizes varies by region.