Paper Size Calculator — ISO & North American Dimensions

Whether you are a graphic designer setting up a print file, a student formatting a university assignment, or an architect preparing technical drawings, knowing the correct paper size dimensions is essential. This guide covers every major paper size ISO A-series, B-series, C-series envelopes, and North American formats with exact measurements in millimeters, centimeters, inches, and pixels at every common DPI setting.

Use the interactive paper size calculator above to convert any sheet size instantly.

What Is a Paper Size Standard?

A paper size standard is an internationally agreed system that defines the exact dimensions of sheets of paper. Standards exist so that documents, envelopes, books, posters, and printed materials work consistently across different printers, copiers, and filing systems around the world.

Two major systems are in use today:

1. ISO 216: The international standard adopted by nearly every country worldwide. It defines the A-series, B-series, and C-series. Originally derived from the German DIN 476 standard introduced in 1922.
2. North American / ANSI: Used primarily in the United States, Canada, and Mexico. Based on traditional inch measurements. Includes Letter, Legal, Ledger/Tabloid, and ANSI A through E sizes.

Quick fact: ISO 216 is used in over 150 countries. The United States, Canada, and Mexico are among the few countries that still primarily use the North American paper system for everyday office documents.

ISO A-Series Paper Sizes — Full Dimensions Chart

The ISO A-series is the most widely used paper size system in the world. It ranges from A0 (the largest) down to A10 (the smallest). Every size is exactly half the area of the one before it, and all sizes share the same aspect ratio of 1:√2 (approximately 1:1.4142).

A4 is the global standard for office documents, letters, invoices, books, and everyday printed matter. It measures 210 × 297 mm — equivalent to 8.27 × 11.69 inches.

A4 at 300 DPI = 2480 × 3508 pixels. This is the standard resolution for professional print-ready PDF documents. For web and screen use, A4 at 72 DPI equals 595 × 842 pixels the default in Adobe Acrobat and most PDF viewers.

The ISO Halving Rule — How ISO Paper Sizes Scale

The most elegant property of ISO paper sizes is the halving rule: fold any ISO sheet in half along its longest edge and you get two sheets of the next smaller size — with exactly the same aspect ratio. This is only possible because of the 1:√2 ratio.

A3 → fold → two A4 sheets A4 → fold → two A5 sheets A5 → fold → two A6 sheets

This halving property makes ISO sizes ideal for printing imposition, booklet creation, large-format scaling, and filing. A document designed for A4 can be scaled up to A3 at exactly 141.4% zoom — or scaled down to A5 at exactly 70.7% — with no distortion and no content loss.

Scaling formula:

• One size up (e.g. A4 → A3): multiply dimensions by √2 ≈ 1.4142
• One size down (e.g. A4 → A5): divide dimensions by √2 ≈ 0.7071

ISO B-Series Paper Sizes

The ISO B-series fills the gaps between A-series sizes. Each B-size is the geometric mean between two consecutive A-sizes. B1 falls between A0 and A1 in area, B2 between A1 and A2, and so on. All B-series sizes share the same 1:√2 aspect ratio as the A-series.

Common uses: B5 is popular for books and notebooks. B4 is used for Japanese newspaper formats. B1 and B2 are standard for large posters and wall charts. B7 matches the dimensions of a standard passport booklet.

ISO C-Series Envelope Sizes

The ISO C-series is designed for envelopes. C-series envelopes are sized to fit the corresponding A-series sheets with just enough clearance for easy insertion. C-series dimensions are defined in ISO 269.

The golden rule of C-series envelopes:

• C4 envelope (229 × 324 mm) — holds a full A4 sheet flat, unfolded
• C5 envelope (162 × 229 mm) — holds an A4 sheet folded once in half
• C6 envelope (114 × 162 mm) — holds an A4 sheet folded twice (to A6 size)

North American Paper Sizes (ANSI / US Standard)

North American paper sizes are based on traditional inch measurements and do not follow the ISO halving rule. The most common is US Letter at 8.5 × 11 inches, which is the default for office documents, word processing, and laser printing across the United States and Canada.

A4 vs US Letter — Side-by-Side Comparison

A4 and US Letter are the two most used paper sizes worldwide. They look almost identical at a glance but differ in ways that matter for printing, design, and document sharing between regions.

Key difference: A4 is taller and slightly narrower than US Letter. Letter is slightly wider and shorter. If you print an A4-formatted document on Letter paper without adjusting margins, the top and bottom of the page may be clipped — and vice versa. Always confirm your paper size setting before exporting a PDF intended for print.

DPI Guide — What Resolution Should You Use for Printing?

DPI (dots per inch) — also called PPI (pixels per inch) for digital screens — determines how many ink dots or pixels are packed into each inch of a printed or displayed image. Higher DPI means sharper text, finer detail, and better image quality, but also larger file sizes.

Rule of thumb: 300 DPI is the minimum at which the human eye cannot distinguish individual dots when reading at a normal distance of approximately 30 cm. Below 300 DPI, text edges appear jagged and fine details look blurry on printed output.

A3 pixel sizes by DPI:

• 72 DPI → 842 × 1191 px
• 150 DPI → 1754 × 2480 px
• 300 DPI → 3508 × 4961 px
• 600 DPI → 7016 × 9921 px

US Letter pixel sizes by DPI:

• 72 DPI → 612 × 792 px
• 150 DPI → 1275 × 1650 px
• 300 DPI → 2550 × 3300 px
• 600 DPI → 5100 × 6600 px

Paper Size Use Cases — What Is Each Format Used For?

Different industries and professions rely on specific paper sizes. Here is a practical reference:

A0 (841 × 1189 mm) Used for architectural plans, engineering drawings, large exhibition posters, billboard source artwork, and construction site documentation.

A1 (594 × 841 mm) Used for presentation posters, academic research posters, movie posters, technical schematics, and large marketing displays.

A2 (420 × 594 mm) Used for event posters, newspaper spreads, large educational wall charts, architectural detail drawings, and maps.

A3 (297 × 420 mm) Used for spreadsheets that need extra columns, folded brochures, architectural sketches, newspaper page layouts, certificates, and design portfolios.

A4 (210 × 297 mm) The global default for office letters, invoices, reports, books, magazines, legal forms, academic papers, and virtually all everyday document printing.

A5 (148 × 210 mm) Used for notebooks, booklets, flyers, greeting cards, diaries, pocket guides, and small promotional brochures.

A6 (105 × 148 mm) Used for postcards, index cards, invitation cards, small pocket notebooks, and compact promotional flyers.

B5 (176 × 250 mm) Popular for books, Japanese magazines, printed manuals, and academic publications. Slightly smaller than A4 and more compact for reading.

US Letter (8.5 × 11 in) Standard for all US office documents, word processing files, laser printing, binders, and business correspondence in North America.

US Legal (8.5 × 14 in) Used for US legal documents, contracts, court filings, government forms, and land records. The extra length accommodates longer agreements.

Tabloid / Ledger (11 × 17 in) Used for newspaper pages, double-page spreads, large restaurant menus, wide brochures, photo prints, and design portfolios.

C4 Envelope (229 × 324 mm) The standard business envelope for mailing A4 documents flat — used for contracts, brochures, and official correspondence that must not be folded.

Frequently Asked Questions About Paper Sizes

What is A4 paper size in inches?

A4 paper is 8.27 × 11.69 inches (210 × 297 mm). It is the standard office paper size used in over 150 countries worldwide. In comparison, US Letter paper measures 8.5 × 11 inches — slightly wider but shorter than A4. At 300 DPI, an A4 document is 2480 × 3508 pixels.

What is A4 size in pixels at 300 DPI?

At 300 DPI (the professional print standard), A4 paper is 2480 × 3508 pixels. At 72 DPI for web and screen use, A4 is 595 × 842 pixels. At 96 DPI (Windows screen default), A4 is 794 × 1123 pixels. At 150 DPI for draft printing, A4 is 1240 × 1754 pixels.

What is A4 size in pixels at 72 DPI?

At 72 DPI — the standard resolution for screen display and PDF viewing — A4 is 595 × 842 pixels. This is the default page size used by Adobe Acrobat, Illustrator, and InDesign when creating documents for on-screen reading.

What is the difference between A4 and A3 paper?

A3 paper is exactly twice the area of A4. A3 measures 297 × 420 mm (11.69 × 16.54 inches), while A4 is 210 × 297 mm. Both share the same 1:√2 aspect ratio. Two A4 sheets placed end-to-end equal one A3 sheet. A3 is commonly used for spreadsheets, brochures, newspaper layouts, and architectural sketches.

Is A4 the same as 8.5 × 11?

No. A4 (210 × 297 mm / 8.27 × 11.69 in) and US Letter (215.9 × 279.4 mm / 8.5 × 11 in) are different sizes. Letter is slightly wider but shorter. They are not interchangeable without margin adjustments. Printing an A4 document on Letter paper without resizing may clip the top and bottom edges.

What envelope size fits an A4 sheet?

A C4 envelope (229 × 324 mm) holds a full A4 sheet flat without folding. A C5 envelope (162 × 229 mm) holds an A4 sheet folded once. A C6 envelope (114 × 162 mm) holds an A4 sheet folded twice to A6 size. These sizes are defined in ISO 269.

Why is 300 DPI the standard for printing?

300 DPI is the minimum resolution at which the human eye cannot see individual ink dots when reading at a normal viewing distance of about 30 cm. Below 300 DPI, text looks jagged and images appear blurry on printed output. Professional offset printers, laser printers, and digital presses are all optimized for 300 DPI input files.

What is the aspect ratio of ISO A-series paper?

All ISO A-series (and B-series) sizes share the aspect ratio 1:√2 ≈ 1:1.4142. This is the only ratio that stays the same when you cut a sheet in half — each half has the same proportions as the whole. This mathematical property makes ISO sizes uniquely practical for scaling, folding, filing, and print imposition.

What paper size is used for passports?

Most passports use the B7 format (88 × 125 mm) from the ISO B-series. The ICAO (International Civil Aviation Organization) specifies passport booklet dimensions as 125 × 88 mm, which matches ISO B7 exactly.

What is the largest standard paper size?

In the ISO A-series, A0 (841 × 1189 mm) is the largest standard size. In the B-series, B0 is larger at 1000 × 1414 mm. For the North American ANSI series, ANSI E at 34 × 44 inches (863.6 × 1117.6 mm) is the largest. Beyond these, architectural and engineering drawings may use custom oversize formats.

How do I convert paper size from mm to inches?

Divide millimeters by 25.4 (since 1 inch = 25.4 mm exactly). Example: A4 width = 210 ÷ 25.4 = 8.27 inches. To convert inches to mm, multiply by 25.4. To get pixel dimensions from mm: pixels = (mm ÷ 25.4) × DPI.

What paper size should I use for a poster?

For standard presentation posters, use A1 (594 × 841 mm). For large exhibition or display posters, use A0 (841 × 1189 mm). For billboard-scale artwork, use B1 (707 × 1000 mm) or larger. In North America, Tabloid (11 × 17 in) is the most common poster size for office and event printing.

All dimensions based on ISO 216, ISO 269, and ANSI/ASME Y14.1 standards. Pixel calculations use the formula: px = (mm ÷ 25.4) × DPI.