# Paper Size Reference > Interactive guide to A-series, Letter, Legal, and envelope sizes with visual comparisons **Category:** Utility **Keywords:** paper, A4, letter, legal, envelope, size, dimensions, print **URL:** https://complete.tools/paper-size-reference ## A-Series Paper Sizes The A-series is defined by ISO 216 and is the most widely used paper size system in the world. It is used across Europe, Asia, Africa, Australia, and most of South America. The defining feature of A-series paper is that each size is exactly half of the next larger size when folded along its longer edge. This means an A4 sheet folded in half becomes A5, and two A4 sheets side by side form an A3. The largest standard size is A0, which has an area of exactly one square meter. Every smaller size is derived by halving the longer dimension: - A0: 841 x 1189 mm, used for large posters and architectural drawings - A1: 594 x 841 mm, used for posters and flip charts - A2: 420 x 594 mm, used for posters and technical drawings - A3: 297 x 420 mm, used for tabloid printing and spreadsheets - A4: 210 x 297 mm, the global standard for everyday documents - A5: 148 x 210 mm, used for notebooks, booklets, and half-sheet flyers - A6: 105 x 148 mm, used for postcards and small notepads - A7: 74 x 105 mm, used for small cards and invitations - A8: 52 x 74 mm, used for mini cards and labels ## US Standard Paper Sizes The United States, Canada, and Mexico use a different set of paper sizes that do not follow the ISO 216 standard. These sizes have their roots in historical paper-making traditions and have been standardized by ANSI (American National Standards Institute). The most commonly used sizes are: - Letter (216 x 279 mm / 8.5 x 11 in): The default paper size for home and office printing in North America. It is slightly wider and shorter than A4. - Legal (216 x 356 mm / 8.5 x 14 in): Used for legal contracts, forms, and government documents. - Tabloid/Ledger (279 x 432 mm / 11 x 17 in): Used for newspapers, newsletters, and larger spreads. Called Tabloid in portrait and Ledger in landscape orientation. - Executive (184 x 267 mm / 7.25 x 10.5 in): A slightly smaller business letter size used for formal correspondence. - Half Letter (140 x 216 mm / 5.5 x 8.5 in): Half of a Letter sheet, used for notepads and small forms. - Government Letter (203 x 267 mm / 8 x 10.5 in): Used for US government documents and forms. - Junior Legal (127 x 203 mm / 5 x 8 in): A smaller notepad size used in legal and office settings. ## Envelope Sizes Envelope sizes are standardized separately from paper sizes, and many envelope formats are designed to fit specific paper sizes when folded. US commercial envelopes are numbered, with higher numbers generally indicating larger sizes. The number 10 envelope (105 x 241 mm) is the most common business envelope in the US. It fits a standard Letter sheet folded in thirds. The number 9 envelope (98 x 225 mm) is slightly smaller and is commonly used as a reply envelope inside a number 10. Invitation envelopes use a different numbering scheme. The A7 envelope (133 x 184 mm) is the most popular for greeting cards and standard invitations. The A6 (121 x 165 mm) and A2 (111 x 146 mm) are used for smaller invitations and cards. ISO C-series envelopes are designed to fit ISO A-series paper without cutting or trimming. C4 (229 x 324 mm) holds an A4 sheet flat. C5 (162 x 229 mm) holds A4 folded once in half. C6 (114 x 162 mm) holds A4 folded twice. The DL envelope (110 x 220 mm) is the most common European business envelope and holds an A4 sheet folded into thirds lengthwise. ## How to use 1. Select a paper category using the tabs at the top: A-Series, US Standard, or Envelopes. 2. Review the size reference table for an overview of all dimensions in that category. 3. Scroll down to the visual comparison to see how the sizes relate to each other in proportion. 4. Click any size rectangle in the visual comparison to open a detailed dimensions panel. 5. The detail panel shows the size in mm, cm, inches, and pixels at 72 DPI, 96 DPI, and 300 DPI. ## FAQs **Q:** What is the difference between A4 and Letter? **A:** A4 (210x297mm / 8.27x11.69 in) is the international standard used in most of the world. US Letter (216x279mm / 8.5x11 in) is slightly wider and shorter. Most modern printers handle both, but default settings vary by region. **Q:** What paper size should I use for printing? **A:** Use A4 if you are in Europe, Asia, Australia, or most of the world. Use Letter if you are in North America. When designing documents for international audiences, A4 is the safer choice since it is more universal. **Q:** What is the most common envelope size? **A:** The number 10 envelope (105x241mm / 4.13x9.5 in) is the standard US business envelope. In Europe, the DL envelope (110x220mm) serves the same role and fits an A4 sheet folded in thirds. **Q:** Why does A4 have those specific dimensions? **A:** A4 dimensions come from a mathematical relationship. The aspect ratio of all A-series paper is 1 to the square root of 2 (approximately 1:1.414). This ensures that when you fold the sheet in half along the longer side, the resulting half-sheet has the same aspect ratio. A0 starts with an area of exactly 1 square meter, and each smaller size is half the previous. **Q:** What DPI should I use for printing? **A:** For standard office printing, 96 DPI is common for screen display. For high-quality photo prints, 300 DPI is the standard. For posters viewed at a distance, 150 DPI may be sufficient. The pixel values shown in this tool help you size your digital files correctly for each use case. **Q:** What is the difference between C4, C5, C6, and DL envelopes? **A:** These are ISO C-series envelopes designed to fit A-series paper. C4 holds A4 flat. C5 holds A4 folded once. C6 holds A4 folded twice (into quarters). DL holds A4 folded in thirds and is the most common European business envelope. --- *Generated from [complete.tools/paper-size-reference](https://complete.tools/paper-size-reference)*