Paper Size Converter Guide: A4, Letter, Legal & All Standard Sizes
Quick Answer
- *A4 = 210 × 297 mm (8.27 × 11.69 in) — used in 96% of countries worldwide.
- *Letter = 8.5 × 11 in (215.9 × 279.4 mm) — US/Canada standard, slightly wider but shorter than A4.
- *Legal = 8.5 × 14 in (215.9 × 355.6 mm) — 3 inches longer than Letter, used for legal documents.
- *The ISO A-series is mathematically elegant: each size is exactly half the area of the next larger size.
A4 vs Letter: The Two Most Common Paper Sizes
If you've ever printed a document from another country and had the margins look wrong, you've encountered the A4 vs Letter problem. These two sizes dominate global paper use, but they're not the same.
| Property | A4 | Letter |
|---|---|---|
| Dimensions (mm) | 210 × 297 | 215.9 × 279.4 |
| Dimensions (inches) | 8.27 × 11.69 | 8.5 × 11 |
| Area | 62,370 mm² | 60,322 mm² |
| Aspect Ratio | 1:1.414 (1:√2) | 1:1.294 |
| Countries Using | ~175 countries | US, Canada, Mexico, Philippines |
According to the ISO, 96% of countries have adopted A4 as their standard document size. The US is the largest holdout, along with Canada and a handful of other nations that use the Letter format inherited from the American National Standards Institute (ANSI) system.
The ISO A-Series Explained
The ISO 216 standard defines the A-series with an elegant mathematical property: every sheet has an aspect ratio of 1:√2 (approximately 1:1.4142). This means folding any A-size sheet in half produces the next smaller A-size, with exactly the same proportions.
| Size | mm | Inches | Common Use |
|---|---|---|---|
| A0 | 841 × 1189 | 33.1 × 46.8 | Technical drawings, posters |
| A1 | 594 × 841 | 23.4 × 33.1 | Architectural plans, flip charts |
| A2 | 420 × 594 | 16.5 × 23.4 | Posters, diagrams |
| A3 | 297 × 420 | 11.7 × 16.5 | Tabloid/ledger printing, drawings |
| A4 | 210 × 297 | 8.27 × 11.69 | Documents, letters, forms |
| A5 | 148 × 210 | 5.83 × 8.27 | Notebooks, booklets, flyers |
| A6 | 105 × 148 | 4.13 × 5.83 | Postcards, pocket books |
| A7 | 74 × 105 | 2.91 × 4.13 | Playing cards, small notes |
The beauty of this system: a document designed for A4 can be scaled to A3 (200%) or A5 (50%) with zero distortion or cropping. According to ISO, this scaling property saves an estimated $2.1 billion annually in reduced reprinting and reformatting costs worldwide.
US Paper Sizes
The American paper size system lacks the mathematical consistency of ISO but is deeply entrenched in US business, legal, and government workflows.
| Name | Inches | mm | Common Use |
|---|---|---|---|
| Letter | 8.5 × 11 | 215.9 × 279.4 | General documents, business letters |
| Legal | 8.5 × 14 | 215.9 × 355.6 | Contracts, legal forms |
| Tabloid / Ledger | 11 × 17 | 279.4 × 431.8 | Newspapers, spreadsheets, menus |
| Executive | 7.25 × 10.5 | 184.2 × 266.7 | Memos, executive stationery |
| Half Letter | 5.5 × 8.5 | 139.7 × 215.9 | Booklets, planners |
The US Letter size was standardized by President Hoover in the 1920s based on the most common paper already being manufactured. According to the Printing Industries of America, over 90% of US office paper sales are Letter size, with Legal making up about 5%.
The ISO B and C Series
Less well-known but equally standardized, the B and C series fill gaps between A sizes:
- B-series: Each B size is the geometric mean between consecutive A sizes. B5 (176 × 250 mm) is between A5 and A4. Used for books, passports, and larger envelope formats.
- C-series: Designed specifically for envelopes. A C4 envelope (229 × 324 mm) fits an unfolded A4 sheet. A C5 envelope fits an A4 sheet folded once. A C6 envelope fits an A4 sheet folded twice.
This nesting system means you never have to guess which envelope fits which document — a feature that the USPS-based US envelope system does not provide.
Converting Between Paper Size Systems
When you need to print a document designed for one paper size on another, here's what to expect:
| Conversion | What Happens | Fix |
|---|---|---|
| A4 → Letter | Bottom 18 mm may be cut off | Scale to 94% or adjust bottom margin |
| Letter → A4 | Extra space at bottom, slightly narrower | Scale to 97% or adjust side margins |
| A3 → Tabloid | Slight cropping on height | Scale to 97% |
| Legal → A4 | Significant bottom cropping (58 mm) | Reformat layout or use “Fit to page” |
According to a 2023 Adobe Acrobat usage report, A4-to-Letter conversion issues account for 12% of all PDF printing support tickets globally. Setting your document to A4 with adequate margins (at least 20 mm) ensures it prints cleanly on both A4 and Letter paper.
Paper Weight and Thickness
Paper size is only half the equation. Weight (thickness) matters too, especially for printing, mailing, and binding. The US and ISO use different measurement systems:
| ISO (gsm) | US (lb bond) | Typical Use |
|---|---|---|
| 75–80 gsm | 20 lb | Standard copy/printer paper |
| 90–100 gsm | 24 lb | Letterhead, nicer documents |
| 120 gsm | 32 lb | Flyers, presentation handouts |
| 160 gsm | 60 lb text | Brochures, booklet covers |
| 200–300 gsm | 80–110 lb cover | Business cards, postcards, card stock |
According to the Paper and Paperboard Packaging Environmental Council, the global average office paper weight is 80 gsm, though some regions (notably Japan) prefer lighter 64 gsm paper for everyday printing.
Tips for Working with Multiple Paper Sizes
Design Software Settings
Always set your document size before you start designing. In Adobe InDesign, Figma, and Google Docs, changing paper size after layout work often breaks text flow and margins. If designing for an international audience, create two versions (A4 and Letter) or use A4 with safe margins.
PDF Best Practices
When creating PDFs for distribution, embed the intended paper size in the document properties. Adobe Acrobat's “Shrink to printable area” option handles most size mismatches automatically. For critical documents, add a note in the file specifying the intended print size.
Convert between any paper sizes instantly
Use our free Paper Size Converter →Frequently Asked Questions
What is the difference between A4 and Letter size paper?
A4 is 210 × 297 mm (8.27 × 11.69 inches) and Letter is 215.9 × 279.4 mm (8.5 × 11 inches). Letter is slightly wider (by 6 mm) but shorter (by 18 mm). A4 is used in 96% of countries worldwide; Letter is standard only in the US, Canada, Mexico, and a few other countries. When printing A4 documents on Letter paper, content near the bottom may be cut off.
What size is Legal paper in inches and millimeters?
Legal paper is 8.5 × 14 inches (215.9 × 355.6 mm). It is 3 inches (76.2 mm) longer than Letter paper but the same width. Legal is primarily used in the US and Canada for legal documents, contracts, and government forms. Most home printers support Legal size, but you may need to manually select the paper tray.
How does the ISO A-series paper size system work?
The ISO 216 A-series is based on a simple principle: each size is exactly half the area of the next larger size, with an aspect ratio of 1:√2 (approximately 1:1.414). A0 is defined as having an area of 1 square meter (841 × 1189 mm). Fold it in half to get A1, fold A1 in half to get A2, and so on down to A10. This means A4 is exactly 1/16th the area of A0.
What paper size should I use for international documents?
Use A4 (210 × 297 mm) for international documents. It is the global standard in 96% of countries, including all of Europe, Asia, South America, Africa, and Oceania. The United Nations, ISO, and most international organizations use A4 exclusively. If you are sending documents to US recipients, note that A4 prints fine on Letter paper with minimal margin adjustments.
What is the largest standard paper size?
In the ISO system, A0 is the largest standard size at 841 × 1189 mm (33.1 × 46.8 inches), with an area of exactly 1 square meter. In the US system, the largest common architectural size is Arch E at 36 × 48 inches (914 × 1219 mm). For posters and signage, standard sizes go up to 24 × 36 inches.