Convert standard paper sizes like A4, A3, A5, Letter, and Legal to millimeters, centimeters, or inches.
Paper size conversion is based on comparing the width-to-height ratio and absolute dimensions of a document to standardized formats.
ISO paper sizes follow the 1:√2 ratio, while US formats use fixed inch-based dimensions. This converter identifies the closest matching standard size.
Yes. Standard paper sizes such as A4, A5, and A3 are defined by fixed international standards, which means they can be converted accurately and directly into millimeters, centimeters, or inches.
This is especially useful for printing, graphic design, international documents, framing, and digital layouts where exact physical dimensions matter.
The ISO 216 standard defines the A-series paper sizes used worldwide. Each size maintains the same aspect ratio, making scaling simple and consistent.
| Paper Size | Millimeters (mm) | Centimeters (cm) | Inches (in) |
|---|---|---|---|
| A3 | 297 × 420 | 29.7 × 42 | 11.69 × 16.54 |
| A4 | 210 × 297 | 21 × 29.7 | 8.27 × 11.69 |
| A5 | 148 × 210 | 14.8 × 21 | 5.83 × 8.27 |
Unlike clothing or shoe sizes, paper sizes are not approximate. ISO paper dimensions are defined using exact metric values. When converting to inches or centimeters, the results remain precise because they are calculated from fixed millimeter measurements.
ISO paper sizes are defined by the international standard ISO 216. The most common size is A4, used globally for letters, documents, and printing.
Each A-size is created by halving the previous size while maintaining the same aspect ratio. This makes scaling documents easy and predictable.
US paper sizes are primarily used in the United States, Canada, and Mexico. The most common formats are Letter and Legal.
Unlike ISO sizes, US paper formats do not follow a consistent ratio, which often causes layout issues when exchanging documents internationally.
| Paper Size | Dimensions (mm) | Dimensions (inches) | Used In |
|---|---|---|---|
| A4 | 210 × 297 | 8.27 × 11.69 | Global documents |
| Letter | 216 × 279 | 8.5 × 11 | US letters |
| Legal | 216 × 356 | 8.5 × 14 | Contracts |
| A3 | 297 × 420 | 11.7 × 16.5 | Posters |
| A5 | 148 × 210 | 5.8 × 8.3 | Notebooks |
No. A4 is taller and narrower than Letter, which can affect printing margins.
ISO sizes are metric-based and optimized for scaling, while US sizes evolved historically using inches.
A4 is recommended for global compatibility.
When placed side by side, A4 appears taller than Letter, while Legal paper extends noticeably further in height. Understanding this prevents layout overflow and cropping.
Searching for A4 size in inches or A3 size in centimeters is common when working across different measurement systems. Because these paper sizes follow ISO standards, conversions are reliable and universally accepted.
This paper size converter allows you to quickly compare international and US paper formats without manual calculations.
Download a full CSV containing ISO and US paper sizes with dimensions in millimeters and inches.