Whether you are printing official documents, selecting envelopes, designing posters, or verifying that a notebook fits inside a backpack compartment, understanding standardized paper dimensions is essential. Most of the modern world relies on the ISO 216 standard (the A-series), while North America predominantly uses traditional formats such as US Letter and US Legal.
The Geometry of the ISO A-Series (The 1:√2 Ratio)
The brilliance of the international A-series paper standard lies in its constant aspect ratio: 1 to √2 (approximately 1 : 1.4142). When an A-series sheet is cut or folded cleanly in half parallel to its shortest side, the two resulting halves have the exact same proportional aspect ratio as the parent sheet.
- A0 is the foundation: an area of exactly 1 square meter (841 × 1189 mm).
- Folding A0 in half yields two sheets of A1 (594 × 841 mm).
- Folding A1 in half yields two sheets of A2 (420 × 594 mm).
- Folding A2 in half yields two sheets of A3 (297 × 420 mm).
- Folding A3 in half yields two sheets of A4 (210 × 297 mm), the global office standard.
- Folding A4 in half produces two sheets of A5 (148 × 210 mm), widely used in compact paperback notebooks.
- Folding A5 in half produces two sheets of A6 (105 × 148 mm), the classic postcard and pocket notepad size.
Complete Paper Dimensions Reference Table
The table below provides precise dimensions for all common formats across metric (millimeters, centimeters) and imperial (inches) units:
| Format | Dimensions (mm) | Dimensions (cm) | Dimensions (inches) | Common Primary Application |
|---|---|---|---|---|
| A0 | 841 × 1189 mm | 84.1 × 118.9 cm | 33.1 × 46.8 in | Technical blueprints, large exhibition posters |
| A1 | 594 × 841 mm | 59.4 × 84.1 cm | 23.4 × 33.1 in | Architectural drawings, academic research posters |
| A2 | 420 × 594 mm | 42.0 × 59.4 cm | 16.5 × 23.4 in | Wall calendars, art prints, diagrams |
| A3 | 297 × 420 mm | 29.7 × 42.0 cm | 11.7 × 16.5 in | Ledger charts, presentations, visual artwork |
| A4 | 210 × 297 mm | 21.0 × 29.7 cm | 8.3 × 11.7 in | Everyday office printing, invoices, official forms |
| A5 | 148 × 210 mm | 14.8 × 21.0 cm | 5.8 × 8.3 in | Notepads, brochures, desk diaries, flyers |
| A6 | 105 × 148 mm | 10.5 × 14.8 cm | 4.1 × 5.8 in | Postcards, pocket memo books, receipt books |
| US Letter | 215.9 × 279.4 mm | 21.6 × 27.9 cm | 8.5 × 11.0 in | Standard North American document printing |
| US Legal | 215.9 × 355.6 mm | 21.6 × 35.6 cm | 8.5 × 14.0 in | North American contracts, legal documentation |
US Letter vs ISO A4: The Packaging Trap
A frequent issue encountered when shipping stationery or organizing binders internationally is the subtle difference between US Letter and ISO A4:
- A4 is narrower (210 mm vs 215.9 mm) but noticeably taller (297 mm vs 279.4 mm).
- US Letter is slightly wider by nearly 6 mm, but shorter by more than 17 mm.
Consequently, an envelope or document sleeve tailored specifically for US Letter paper may fail to close when holding an A4 sheet because the top edge protrudes. Before ordering packaging or binders, always check clearance tolerances using the 2D Fit Checker.
Checking if your document fits in a folder or box?
Use our interactive tool to calculate clearance margins and 90° orientation fit.
Open 2D Fit CheckerFrequently Asked Questions
Why is A4 the most widespread paper size?
A4 struck the optimal compromise for human reading ergonomics and typewriter/printer carriage widths during the 20th century. Its adoption by the United Nations and ISO solidified it as the global standard.
What margin should I leave when packing paper in boxes?
We recommend at least 10 mm to 15 mm of clearance on each side. Paper sheets expand slightly with atmospheric humidity, and protective cardboard corners require buffer room to prevent dog-eared corners.
Can I measure small paper scraps on this site?
Yes. If you have an unlabelled card or paper fragment, you can measure its exact width and height directly using the Online Screen Ruler.