Paper Size Converter
Convert paper sizes to mm, cm, and inches instantly — A0 through A10, B0 through B10, C0 through C10 (envelopes), US Letter, Legal, Tabloid, and ANSI sizes. Includes diagonal calculation and a full series comparison table. Free, private, and 100% client-side. No signup required.
Select any paper size and unit to see exact dimensions and diagonal. Browse the full comparison table for A, B, C, and US series. All calculations run instantly in your browser — no data sent to any server.
Common use: Standard office paper worldwide
Sizes are shown proportionally relative to A4 (capped at 120px for very large sizes).
| Size | Width (mm) | Height (mm) | Diagonal (mm) |
|---|---|---|---|
| A0 | 841.0 | 1189.0 | 1456.4 |
| A1 | 594.0 | 841.0 | 1029.6 |
| A2 | 420.0 | 594.0 | 727.5 |
| A3 | 297.0 | 420.0 | 514.4 |
| A4 | 210.0 | 297.0 | 363.7 |
| A5 | 148.0 | 210.0 | 256.9 |
| A6 | 105.0 | 148.0 | 181.5 |
| A7 | 74.0 | 105.0 | 128.5 |
| A8 | 52.0 | 74.0 | 90.4 |
| A9 | 37.0 | 52.0 | 63.8 |
| A10 | 26.0 | 37.0 | 45.2 |
Click any row to select that size and see its full dimensions above.
The most complete paper size converter online — covers all ISO A, B, and C series plus US sizes, with mm, cm, and inch output and diagonal calculation.
Instant Paper Size Conversion
Convert any paper size — A0 through A10, B0 through B10, C0 through C10, US Letter, Legal, Tabloid, and ANSI sizes — to mm, cm, or inches instantly. Diagonal is calculated automatically using the Pythagorean theorem.
Full Series Comparison Table
Browse the complete A, B, C, and US series side by side in a sortable table. Click any row to select that size and see its full dimensions. Switch units and the entire table updates instantly.
Secure Paper Size Converter Online
Every paper size lookup and unit conversion runs entirely in your browser using client-side JavaScript. Your selections never leave your device — complete privacy, zero server uploads.
100% Free — No Signup Required
The paper size converter is completely free with no account, no ads, and no usage limits. Look up any paper size in any unit as many times as you need, any time, on any device.
See how designers, printers, students, and office professionals use the paper size converter in their daily workflows.
Print & Document Setup
Set up print documents in design software like Adobe InDesign, Illustrator, or Canva. Use the paper size converter to get exact mm or inch dimensions for A4, A3, US Letter, or any other paper size before creating your artboard.
Photo Printing & Framing
Photographers and artists use the paper size converter to match print sizes to standard frame dimensions. Convert A4 to inches to find the right frame, or check if a B5 print fits a standard photo frame.
Packaging & Product Design
Packaging designers use the paper size converter to plan box inserts, instruction leaflets, and product labels. Convert between mm and inches to match international printing specifications and supplier requirements.
Education & Stationery
Teachers and students use the paper size converter to understand the difference between A4 and US Letter, or to find the right paper size for notebooks, worksheets, and exam papers across different countries.
Envelope & Mailing
Use the C-series sizes to find the right envelope for any ISO document. The paper size converter shows which C-series envelope fits each A-series document — C4 for A4 unfolded, C5 for A4 folded once, C6 for A4 folded twice.
Digital Design & Screen Layouts
Web and UI designers use the paper size converter to create digital mockups at real-world print dimensions. Convert A4 to pixels at 72, 96, or 300 DPI by first getting the inch dimensions from the paper size converter.
A complete reference guide to ISO paper size series, US paper sizes, and how the diagonal calculation works.
What is Paper Size Conversion?
Paper size conversion is the process of expressing the same paper dimensions in a different unit — for example, converting A4 from millimetres (210 × 297 mm) to inches (8.268 × 11.693 in). The paper size converter stores all dimensions in millimetres as the base unit and converts to cm or inches using the exact factors: 1 inch = 25.4 mm, 1 cm = 10 mm. The diagonal is calculated using the Pythagorean theorem: diagonal = √(width² + height²), giving the corner-to-corner measurement useful for screen size comparisons and frame fitting.
How Our Paper Size Converter Works
- 1Select a paper size: Choose from the dropdown (A0–A10, B0–B10, C0–C10, US Letter, Legal, Tabloid, ANSI, and more), or click any row in the comparison table.
- 2Choose your unit: Switch between mm, cm, and inches. The result card and the full comparison table both update instantly.
- 3Read your dimensions: The result card shows width, height, and diagonal in your chosen unit, plus all three units side by side for quick reference.
Paper Size Series Explained
- ISO A-Series: The most widely used paper sizes globally. A0 has an area of exactly 1 m². Each smaller size is half the area of the previous: A1 = half of A0, A2 = half of A1, etc. All A-series sizes share the same √2 (≈1.414) aspect ratio.
- ISO B-Series: Intermediate sizes between A-series. B0 = 1,000 × 1,414 mm. Used for posters, books, and newspapers. Each B size is the geometric mean of the adjacent A sizes.
- ISO C-Series (Envelopes): Designed to hold A-series documents. C4 holds A4 unfolded, C5 holds A4 folded once, C6 holds A4 folded twice. C-series sizes are the geometric mean of A and B sizes.
- US / North American Sizes: US Letter (8.5 × 11 in) is the standard US office paper, slightly wider and shorter than A4. US Legal (8.5 × 14 in) is used for legal documents. ANSI sizes (A–E) are used for engineering drawings.
A4 vs. US Letter
A4 (210 × 297 mm / 8.27 × 11.69 in) is taller and narrower than US Letter (215.9 × 279.4 mm / 8.5 × 11 in). A4 is the standard in Europe, Asia, and most of the world. US Letter is standard in the US and Canada.
The √2 Aspect Ratio
All ISO A, B, and C series sizes share the √2 aspect ratio (≈1.414). This means folding a sheet in half always produces the next smaller size with the same proportions — A4 folded = A5, A3 folded = A4.
Diagonal Calculation
The diagonal is calculated using the Pythagorean theorem: d = √(w² + h²). For A4: d = √(210² + 297²) ≈ 363.8 mm ≈ 14.32 in. Useful for comparing paper sizes to screen sizes and finding the right frame.
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A paper size converter is a tool that shows the dimensions of standard paper sizes in different units — mm, cm, or inches — and calculates the diagonal. Our paper size converter covers all ISO A-series (A0–A10), B-series (B0–B10), C-series (C0–C10), and US sizes (Letter, Legal, Tabloid, ANSI A–E) and runs entirely in your browser with no signup required.
A4 paper is 210 × 297 mm, which equals 8.268 × 11.693 inches (or approximately 8.27 × 11.69 in). The diagonal of A4 is approximately 363.8 mm or 14.32 inches. Use the paper size converter above to see A4 in mm, cm, or inches instantly.
A4 (210 × 297 mm / 8.27 × 11.69 in) is taller and narrower than US Letter (215.9 × 279.4 mm / 8.5 × 11 in). A4 is the standard paper size in Europe, Asia, Australia, and most of the world. US Letter is the standard in the United States and Canada. Documents formatted for one size may have small margins or clipping when printed on the other.
A3 paper is 297 × 420 mm, which equals 11.693 × 16.535 inches. A3 is exactly twice the area of A4 — two A4 sheets placed side by side equal one A3 sheet. A3 is commonly used for spreadsheets, architectural drawings, and posters.
C4 envelopes (229 × 324 mm) fit A4 paper unfolded. C5 envelopes (162 × 229 mm) fit A4 paper folded once in half. C6 envelopes (114 × 162 mm) fit A4 paper folded twice (into quarters). The C-series is specifically designed to hold A-series documents.
The diagonal is calculated using the Pythagorean theorem: diagonal = √(width² + height²). For A4: diagonal = √(210² + 297²) = √(44,100 + 88,209) = √132,309 ≈ 363.8 mm ≈ 14.32 inches. The paper size converter calculates this automatically for every size and unit.
All ISO A, B, and C series paper sizes have a width-to-height ratio of 1:√2 (approximately 1:1.4142). This special ratio means that folding a sheet in half always produces the next smaller size with the same proportions. For example, folding A4 in half gives A5, and folding A3 in half gives A4.
Yes, completely. All paper size lookups and unit conversions are performed locally in your web browser using client-side JavaScript. No selections, inputs, or results are ever sent to any server. Your data stays entirely on your device.
Yes. The paper size converter is 100% free with no account registration, no payment, and no usage limits. Look up any paper size in any unit as many times as you need, any time, on any device.