What is the A-series paper standard?

The A-series is the most widely used paper size standard in the world, defined by ISO 216. Every size maintains a √2 aspect ratio, so folding any size in half gives the next size down.

Why is A0 the base size?

A0 has an area of exactly 1 square metre (841 × 1189 mm). All other A sizes are derived by halving the previous size, which is why A4 is 1/16th of A0.

A4 (210 × 297 mm) is the most common paper size worldwide. It's used for letters, documents, magazines, forms, and almost all general printing in the UK and Europe.

What is the smallest A-series size?

A10 (26 × 37 mm) is the smallest A-series size. It's rarely used commercially but is part of the standard.

A-Series Paper Guide 2026 – A0 to A10 Complete

A-Series Paper Sizes: The Complete Guide

The A-series is the world's most popular paper size system, used in over 200 countries. From A0 posters to A10 business cards, every A-series size is part of an elegant mathematical system defined by ISO 216.

📊 Quick Facts:
• Standard: ISO 216
• Aspect ratio: 1:√2 (1:1.414) for every size
• Base size: A0 = 1 square metre
• Most common: A4 (used by billions daily)
• Largest: A0 (841 × 1189 mm)
• Smallest: A10 (26 × 37 mm)

📏 Complete A-Series Dimensions

Size	Millimetres	Inches	Common Uses
A0	841 × 1189 mm	33.1 × 46.8 in	Large posters
A1	594 × 841 mm	23.4 × 33.1 in	Posters, technical drawings
A2	420 × 594 mm	16.5 × 23.4 in	Wall charts, art prints
A3	297 × 420 mm	11.7 × 16.5 in	Posters, spreadsheets
A4	210 × 297 mm	8.3 × 11.7 in	Letters, documents, forms
A5	148 × 210 mm	5.8 × 8.3 in	Notebooks, flyers
A6	105 × 148 mm	4.1 × 5.8 in	Postcards, cards
A7	74 × 105 mm	2.9 × 4.1 in	Tags, mini cards
A8	52 × 74 mm	2.0 × 2.9 in	Business cards (small)
A9	37 × 52 mm	1.5 × 2.0 in	Small labels
A10	26 × 37 mm	1.0 × 1.5 in	Miniature prints

🧠 The Mathematics Behind the A-Series

The genius of the A-series lies in its √2 aspect ratio (approximately 1:1.414). This means:

Folding in half gives the next size down (A3 → A4 → A5)
Doubling gives the next size up (A4 → A3 → A2)
Every size has the same proportions — no distortion when scaling
Zero waste — cutting standard sizes gives no offcuts

The base is A0, which has an area of exactly 1 square metre. Every size halves the area of the previous one.

🎨 Common Uses for Each A-Size

A0–A1: Large Format

Trade show displays
Architectural plans
Large technical drawings
Cinema and event posters

A2–A3: Medium Format

Wall charts and diagrams
Spreadsheets and diagrams
Art prints
Presentation boards

A4: The Global Standard

Letters and business correspondence
Magazines and printed documents
Forms and official documents
School and university work
Standard printer paper

A5–A10: Small Format

Notebooks and diaries
Flyers and leaflets
Postcards and greeting cards
Business cards and tags

🖨️ A-Series Paper Weights

Common paper weights in the UK (in gsm — grams per square metre):

GSM	Best For
80 gsm	Standard printer paper
100 gsm	Letterheads, invoices
120 gsm	Brochures, flyers
160 gsm	Posters, photos
250 gsm	Business cards, invitations
350 gsm	Premium business cards

🔁 A-Series Conversions

Use our conversion tools to move between sizes:

A4 to A3 (double)
A3 to A4 (half)
A4 to A5 (half)
A5 to A4 (double)
A4 to Pixels
A3 to Pixels

🌍 A-Series Around the World

UK & Europe: A4 is standard for letters and documents
USA: A4 is uncommon — Letter is used instead
Australia & Asia: A4 is used (following European standard)
Global: A4 is recognised everywhere for international documents

A-Series Paper Guide