What is the difference between A4 and Letter paper size?

A4 and Letter are similar but not identical. A4 (210×297mm or 8.27×11.69 inches) is the international standard used in most countries, while Letter (216×279mm or 8.5×11 inches) is the North American standard. A4 is 6mm (0.23 inches) narrower but 18mm (0.71 inches) taller than Letter. This means A4 appears slimmer and taller, while Letter is wider and shorter. The aspect ratio also differs: A4 uses the √2 ratio (1:1.41) while Letter uses 1:1.29. This matters when printing documents - an A4 document printed on Letter paper may have the bottom cut off, and vice versa. When sharing documents internationally, always check the page size and adjust margins if needed. Most modern PDF viewers can scale to fit the target paper size.

Why do A4, A5, A6 paper sizes follow that naming pattern?

The ISO A series follows a mathematical system where each size is exactly half the area of the previous size. A0 is the largest (841×1189mm, roughly 1 square meter). When you fold A0 in half, you get A1. Fold A1 in half, you get A2, and so on. A4 is four folds smaller than A0. The genius of this system is the √2 (1.414) aspect ratio - when you cut any A size paper in half, you get two sheets of the next smaller size with the exact same proportions. This means A4 folded in half becomes A5, A5 folded becomes A6, etc. This makes photocopying, scaling, and document design much easier since proportions never change. Two A4 pages scaled to 141% become exactly one A3 page with no distortion.

Can I print an A4 document on Letter paper or vice versa?

Yes, but with caveats. If printing an A4 document on Letter paper, you'll have unused space since A4 is taller. This is the safer direction. However, printing a Letter document on A4 paper will cut off the sides since Letter is wider. To handle this, most printers offer 'Scale to fit' or 'Fit to page' options that shrink the document slightly to fit the target paper. This may make text smaller and affect readability. For important documents, it's best to redesign for the target paper size in your document editor by changing the page size in the page setup settings. Always preview before printing. For PDFs being shared internationally, consider providing both A4 and Letter versions, or note the intended paper size prominently so recipients can adjust their printer settings accordingly.

What paper size should I use for international documents?

Use A4 (210×297mm) for international documents as it's the standard in over 150 countries including all of Europe, Asia, South America, Africa, and Oceania. Only North America (USA, Canada, Mexico) primarily uses Letter size. A4 is the ISO standard (ISO 216) and is universally recognized in international business, education, and government. If your audience is specifically in the United States or Canada, use Letter (8.5×11 inches) as that's what they expect and what their printers are configured for. For documents going to both audiences, create two versions or use A4 as the default since it's more widely used globally. Most modern printers worldwide support both A4 and Letter, so technical compatibility isn't usually an issue - it's more about meeting expectations and ensuring proper formatting.

Why doesn't the United States use A4 paper like the rest of the world?

The US established its paper size standards long before the ISO metric system was created. Letter size has been used in North America since the 1600s-1700s, based on traditional papermaking methods and imperial measurements. When the ISO A series was introduced in 1975 as an international standard, the US already had a massive installed base of Letter-sized documents, filing systems, printers, and business processes. Converting would have required enormous costs for businesses, governments, and individuals to replace equipment, redesign documents, and restructure filing systems. Multiple attempts to switch the US to the metric system (including paper) have been proposed but failed due to costs and resistance to change. The rest of the world adopted A4 during modernization or had less invested in legacy systems. Today, the printing industry must support both standards, and digital PDFs have made size differences less problematic.

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Convert Paper Sizes Instantly (A4, Letter, Legal — mm, cm, inches)

Convert between international paper sizes (A4, Letter, Legal) with dimensions in mm, cm, and inches. Compare ISO A/B series and North American paper standards.

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How to Use Paper Size Converter

Find Paper Dimensions

Select Paper Category: Choose size standard
- ISO A Series: A4, A3, A5 (international standard)
- ISO B Series: B4, B5 (intermediate sizes)
- North American: Letter, Legal, Tabloid
- Other Standards: Envelope sizes (C4, C5)
- Each category has different sizes
Select Paper Size: Pick your paper size
- Drop-down shows available sizes
- Each category has specific sizes
- Most common: A4, Letter, A3, Legal
- Names indicate size within series
- Quick selection from list
View Dimensions: See all measurements
- Millimeters (mm): Metric standard
- Centimeters (cm): Convenient metric
- Inches (in): Imperial measurement
- Aspect Ratio: Width to height ratio
- Common Use: What it's typically used for
- Colorful gradient display
Use Quick Examples: Try common sizes
- A4 (210×297 mm) - International standard
- Letter (8.5×11") - US standard
- A3 (297×420 mm) - Large format
- Legal (8.5×14") - Legal documents
- One-click loading
Compare A4 vs Letter: See the difference
- Side-by-side comparison
- Dimension differences highlighted
- Regional usage information
- Aspect ratio comparison
- Margin adjustment notes

Features

Four Paper Categories

ISO A Series:

A0, A1, A2, A3, A4, A5, A6, A7
International standard (ISO 216)
Based on √2 (1.414) ratio
Each size is half the previous
Used worldwide except North America
A4 most common (210×297 mm)

ISO B Series:

B4, B5 sizes
Intermediate between A sizes
B4 between A3 and A4
Used for books, passports
Less common than A series
Also follows √2 ratio

North American:

Letter, Legal, Tabloid, Executive
Standard in USA, Canada, Mexico
Based on imperial measurements
Letter most common (8.5×11")
Different aspect ratios than ISO
Not based on consistent ratio

Other Standards:

C4, C5 envelope sizes
Designed to fit A series paper
C4 envelope fits A4 paper
C5 envelope fits A5 paper
Follows envelope standards

Multiple Unit Measurements

Millimeters (mm):

Standard metric unit
Most precise
Used in design/printing
ISO sizes defined in mm
International standard

Centimeters (cm):

Convenient metric unit
Easier for visualization
Divide mm by 10
Common in education
Practical for everyday use

Inches (in):

Imperial measurement
Standard in North America
Used for Letter, Legal sizes
Convert: 1 inch = 25.4mm
Familiar to US users

Aspect Ratio:

Width to height proportion
ISO A/B series: 1:√2 (1:1.41)
Letter: 1:1.29
Affects scaling and folding
Important for document design

Complete Reference Tables

All paper sizes organized by category:

Size name and dimensions
All measurement units
Common use cases
Easy comparison
Grouped by standard
Printable reference

A4 vs Letter Comparison

Special comparison section:

Most common international confusion
Side-by-side dimensions
Regional usage
Margin implications
Conversion notes
Visual size difference

Paper Size Tips

10 essential tips included:

A4 worldwide standard
Letter US standard
ISO √2 ratio explained
Size difference details
Folding relationships
Series purpose
Printer compatibility
Document conversion
Margin adjustments

Understanding Paper Sizes

ISO A Series Explained

The √2 Ratio:

Each size has aspect ratio 1:√2 (1:1.414)
Mathematical perfection
Folding in half maintains ratio
A4 folded = A5 (same shape)
A5 folded = A6, and so on
Scales proportionally

Size Progression:

A0 = 1 square meter area (841×1189mm)
A1 = A0 folded in half (594×841mm)
A2 = A1 folded in half (420×594mm)
A3 = A2 folded in half (297×420mm)
A4 = A3 folded in half (210×297mm)
A5 = A4 folded in half (148×210mm)
Each has exactly half the area

Why √2 Ratio Matters:

Photocopying maintains proportions
2 A4 pages = 1 A3 page (scale 141%)
2 A5 pages = 1 A4 page
No distortion when scaling
Professional document workflow
Standard for printing industry

Global Adoption:

Used in 195+ countries
ISO 216 standard (1975)
Universal except North America
All metric countries
Business, education, government
Printing and publishing

North American Sizes Explained

Letter Size (8.5 × 11"):

Most common in USA/Canada
216 × 279 mm metric
Ratio 1:1.29 (not √2)
Based on imperial measurements
Standard for documents, letters
Home printer default

Legal Size (8.5 × 14"):

3 inches taller than Letter
216 × 356 mm metric
Used for legal documents
Contracts, court papers
Longer format needed
Same width as Letter

Tabloid/Ledger (11 × 17"):

Double Letter size
279 × 432 mm metric
Newspapers, large spreadsheets
Architectural drawings
Requires large-format printer
Also called Ledger when landscape

Historical Origin:

Based on traditional papermaking
Imperial measurements
No mathematical relationship
Predates metric system
Customary in North America
Never adopted ISO standard

A4 vs Letter: The Key Difference

Dimensional Comparison:

A4: 210 × 297 mm (8.27 × 11.69")
Letter: 216 × 279 mm (8.5 × 11")
A4 is 6mm (0.23") narrower
A4 is 18mm (0.71") taller
Different aspect ratios
Not directly interchangeable

Visual Difference:

A4 appears taller and slimmer
Letter appears wider and shorter
A4: portrait-oriented feel
Letter: more square feel
Noticeable when compared
Affects document layout

Practical Implications:

Documents don't print identically
Margins may need adjustment
Text reflow required
Images may need resizing
Page count can change
Check printer settings

Conversion Issues:

PDF designed for Letter on A4 = margins cut
A4 PDF on Letter = unused space
Scale to fit: text becomes smaller
Fit to page: distortion possible
Best: redesign for target size
Preview before printing

ISO B Series Purpose

What is B Series:

Intermediate sizes between A series
B4 is between A3 and A4
B5 is between A4 and A5
Also follows √2 ratio
Width of Bn = geometric mean of An and A(n-1)
Less commonly used

Common Uses:

B5: books, passports, comic books
B4: newspapers, folders
Printing and publishing
When A series too large or small
Professional documents
Regional variations exist

B Series Dimensions:

B4: 250 × 353 mm
B5: 176 × 250 mm
Larger than equivalent A size
Maintains proportion
Specialized applications

C Series Envelopes

Purpose of C Series:

Designed specifically for envelopes
C4 envelope fits A4 paper unfolded
C5 envelope fits A5 paper (or A4 folded once)
C6 envelope fits A6 paper (or A4 folded twice)
Perfect fit system
International mailing standard

Dimensions:

C4: 229 × 324 mm (for A4)
C5: 162 × 229 mm (for A5)
C6: 114 × 162 mm (for A6)
Sized between A and B series
Standardized mailing

Paper Size Selection Guide

For Documents

Standard Documents:

A4: International business, letters, reports
Letter: North American documents
Legal: Contracts, legal briefs, compliance docs
A5: Booklets, programs, flyers
Executive: Planners, small reports

Large Documents:

A3: Diagrams, drawings, spreadsheets
Tabloid: Newspapers, presentations
A2: Posters, charts, technical drawings
A1: Architectural plans, large posters
A0: Engineering drawings, large posters

Small Documents:

A6: Postcards, notecards, invitations
A7: Business cards, small notes
A5: Notebooks, leaflets, mini brochures

For Printing

Home Printers:

Most support Letter and A4
Some support Legal
Check specifications for A3/Tabloid
Consumer printers: typically Letter/A4/Legal
Professional printers: wider range

Commercial Printing:

Full range of ISO sizes
Custom sizes available
Large format (A0, A1)
Standard press sheets
Efficient paper usage

Photo Printing:

Different standards (4×6", 5×7", 8×10")
Not A series or Letter
Based on photo ratios
Special photo paper
Crop to fit may be needed

For International Use

Global Documents:

Use A4 for international audience
Safest choice worldwide
Universal recognition
Standard business size
Accepted everywhere

North American Audience:

Use Letter for US/Canada
Legal for contracts
Local standard expected
Printer compatibility
Familiar format

Mixed Audience:

Choose target region
Or provide both formats
Digital: PDF scalable
Note size in document
Test printing both

Common Use Cases

Document Creation

Writing in Microsoft Word:

Default often Letter (US) or A4 (international)
Change in Page Setup/Layout
Set before writing
Affects margins, layout
Choose based on audience

Creating PDFs:

Set page size before export
Common issue: wrong size
Recipient may have different default
Specify size in filename
Test print before sending

Designing Documents:

Choose size first
Affects layout decisions
Consider final output
Printer limitations
Bleeds and margins

Printing Challenges

A4 Document on Letter Printer:

Bottom 18mm will be cut off
Or use "Scale to fit" (text smaller)
Adjust margins before printing
Or redesign for Letter
Preview essential

Letter Document on A4 Printer:

Will fit, but with extra white space
Not cut off (A4 is taller)
May look awkward
Margins uneven
Less problematic than reverse

International Collaboration:

Team uses different standards
Agree on size at start
Use cloud tools (auto-adjust)
Or share PDFs (locked layout)
Consider final output location

Buying Paper

Office Supply Shopping:

Know your region's standard
USA: buy Letter (8.5×11")
Europe/Asia: buy A4 (210×297mm)
Check printer manual
Multi-purpose paper vs specialty

Printer Specifications:

Check supported sizes
Most: Letter, A4, Legal
Some: A3, Tabloid
Photo sizes separate
Manual feed for odd sizes

International Ordering:

Paper sizes vary by region
US store = Letter default
European store = A4 default
Specify size clearly
Check dimensions, not just name

Interesting Facts

A4 origin: German standard (1922), became ISO standard (1975)
Letter origin: Traditional US papermaking, possibly from medieval times
A0 size: Exactly 1 square meter in area (well, 0.999949 m²)
Perfect halving: A series only paper standard where folding perfectly halves the size
Global adoption: 95% of world uses A4, only North America primarily uses Letter
Cost efficiency: A series minimizes waste when cutting from large sheets
Mathematics: √2 ratio discovered as optimal for scaling by German engineer (1920s)
US resistance: Multiple attempts to switch USA to A4 have failed
Printer industry: Must manufacture for both standards due to US market
Digital age: PDF format supports all sizes, reducing conversion issues

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