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Paper Size Converter

Convert between paper sizes (A series, B series, US sizes) and units

A4 Dimensions

Width

210 mm

Height

297 mm

Area

62,370 mm²

Paper Size Reference

Sizemminches
A0841 × 118933.11 × 46.81
A1594 × 84123.39 × 33.11
A2420 × 59416.54 × 23.39
A3297 × 42011.69 × 16.54
A4210 × 2978.27 × 11.69
A5148 × 2105.83 × 8.27
A6105 × 1484.13 × 5.83
A774 × 1052.91 × 4.13
A852 × 742.05 × 2.91
B01000 × 141439.37 × 55.67

What is Paper Size Conversion?

Paper size conversion translates dimensions between different standard paper formats used around the world. The two dominant systems are the ISO A and B series (used internationally) and the US paper sizes (Letter, Legal, Tabloid) used primarily in North America. Understanding these standards and their dimensions is essential for printing, document preparation, and graphic design.

The ISO A series is based on a elegant mathematical principle: each size is exactly half the area of the previous size when cut parallel to the shorter side. A0 has an area of exactly 1 square meter, A1 is half that (0.5 m²), A2 is a quarter, and so on down to A8. The aspect ratio of all A-series sizes is always 1:√2 (approximately 1:1.4142), which means the proportions remain constant regardless of size.

The B series provides intermediate sizes between the A series, useful when you need a size between two A formats. US sizes (Letter at 8.5 × 11 inches, Legal at 8.5 × 14 inches, and Tabloid at 11 × 17 inches) do not follow the ISO mathematical system and have different proportions. This converter helps you navigate between all these standards and view dimensions in millimeters, centimeters, inches, or points.

Paper Size Dimensions

The ISO A-series dimensions follow a precise mathematical relationship based on the square root of 2.

ISO A-Series Dimension Formula

Width(A_n) = A0_width / 2^(n/2), Height(A_n) = A0_height / 2^(n/2)

Where:

  • A0_width= 841 mm — the width of A0 paper
  • A0_height= 1189 mm — the height of A0 paper
  • n= The A-series size number (0 through 8)
  • 1:√2= The constant aspect ratio of all A-series sizes

Standard Paper Sizes Reference

The following table lists the most commonly used paper sizes with their dimensions in both millimeters and inches.

Size Millimeters Inches Common Use
A4210 × 2978.27 × 11.69International standard documents
Letter215.9 × 279.48.5 × 11US standard documents
Legal215.9 × 355.68.5 × 14US legal documents
A3297 × 42011.69 × 16.54Posters, large spreadsheets
Tabloid279.4 × 431.811 × 17Newspapers, large graphics

How to Use This Calculator

Converting paper sizes is straightforward:

  1. Select a paper size: Choose from the dropdown menu, organized by ISO A series, ISO B series, and US sizes.
  2. Choose display unit: Select whether you want dimensions in millimeters, centimeters, inches, or typographic points.
  3. View dimensions: The calculator displays width, height, and area in your selected unit.
  4. Use the reference table: Compare all standard sizes at a glance using the comprehensive reference table.

Real-World Applications

Paper size conversion is essential in international business and publishing. Documents created on US Letter paper (8.5 × 11 inches) do not fit correctly in A4 printers used in Europe and Asia, and vice versa. When sending documents internationally, converting between these formats ensures proper printing without scaling, cropping, or formatting errors.

In graphic design and print production, understanding paper sizes determines layout dimensions, margin settings, and image resolutions. A designer creating an A3 poster needs to know that it measures 297 × 420 mm (11.69 × 16.54 inches) to set up their document correctly. Print shops worldwide work with both ISO and US sizes, making conversion knowledge essential for accurate quoting and production.

Office productivity benefits from paper size awareness. Setting the wrong paper size in printer settings causes documents to print incorrectly — text may be cut off, margins may be wrong, or pages may not fit the paper at all. Understanding that A4 (210 × 297 mm) is slightly taller and narrower than US Letter (215.9 × 279.4 mm) helps users configure their software correctly for their location.

Worked Examples

Converting A4 to Inches

Problem:

What are the dimensions of A4 paper in inches?

Solution Steps:

  1. 1A4 dimensions in mm: 210 × 297 mm
  2. 2Convert width: 210 ÷ 25.4 = 8.27 inches
  3. 3Convert height: 297 ÷ 25.4 = 11.69 inches

Result:

A4 = 8.27 × 11.69 inches

Converting US Letter to Millimeters

Problem:

What are the dimensions of US Letter paper in millimeters?

Solution Steps:

  1. 1US Letter dimensions: 8.5 × 11 inches
  2. 2Convert width: 8.5 × 25.4 = 215.9 mm
  3. 3Convert height: 11 × 25.4 = 279.4 mm

Result:

US Letter = 215.9 × 279.4 mm

Comparing A4 and Letter

Problem:

How do A4 and US Letter paper sizes compare?

Solution Steps:

  1. 1A4: 210 × 297 mm (8.27 × 11.69 in)
  2. 2Letter: 215.9 × 279.4 mm (8.5 × 11 in)
  3. 3Letter is wider (215.9 vs 210 mm) but shorter (279.4 vs 297 mm)
  4. 4A4 has an area of 62,370 mm²; Letter has 60,324 mm²

Result:

A4 is narrower but taller than US Letter

Tips & Best Practices

  • ✓A4 (210 × 297 mm) is the international standard — know its dimensions
  • ✓US Letter (8.5 × 11 in) is NOT the same as A4 — they have different proportions
  • ✓A series sizes always have a 1:√2 aspect ratio, so they scale perfectly
  • ✓Set your printer's paper size correctly to avoid formatting issues
  • ✓When sending documents internationally, check which paper size the recipient uses
  • ✓Points (pt) are used in typography: 1 inch = 72 points

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Frequently Asked Questions

A4 is the international standard because of its elegant mathematical design. The ISO 216 standard defines A0 as exactly 1 square meter with a 1:√2 aspect ratio. Each subsequent A size is half the area of the previous one while maintaining the same proportions. This system was adopted by most countries worldwide, with the US being a notable exception.
A4 is slightly taller than US Letter (11.69 inches vs 11 inches), so printing A4 on Letter may cut off the bottom of the document. The widths are close (8.27 vs 8.5 inches), so horizontal content usually fits. For best results, always match your document size to your paper size or adjust scaling in printer settings.
A3 (297 × 420 mm) is exactly twice the area of A4 (210 × 297 mm). In practice, A3 is what you get when you place two A4 sheets side by side along their shorter edges. A3 is commonly used for posters, architectural drawings, and large spreadsheets.
Most countries outside the United States use the ISO A series, with A4 being the standard for documents. Canada, Mexico, the Philippines, and a few other countries also use US Letter. Japan uses the JIS B series alongside the ISO A series. Understanding which system a country uses helps with international document preparation.
ISO B-series sizes provide intermediate dimensions between consecutive A-series sizes. B1 is between A0 and A1, B2 is between A1 and A2, and so on. B sizes are commonly used for books, posters, and envelopes. The B series is defined by taking the geometric mean of consecutive A sizes, giving practical intermediate dimensions.

Sources & References

Last updated: 2026-06-06

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Editorial Note

MyCalcBuddy Editorial Team

This page is maintained as an educational calculator reference.

Source

Formula Source: NIST Guide to SI Units

by National Institute of Standards

UpdatedLast reviewed: May 2026
CheckedFormula checks are based on standard references and internal QA review.