Units & Conversions
Paper Size Converter - Convert between paper size standards
Convert between paper size standards
Formulas and edge cases are reviewed against authoritative references before publication. For methodology, editorial standards, or corrections, use the links below.
Frequently asked questions
What is the ISO A series?
A0 is 1 m². Each subsequent size is half: A1 = A0/2, A2 = A1/2, etc.
US Letter vs A4?
Letter: 8.5×11 in (216×279mm). A4: 210×297mm. A4 is slightly narrower and taller.
What's the √2 ratio?
ISO sizes maintain aspect ratio when halved. This only works with √2:1 ratio.
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About this tool
Use this Paper Size Converter to convert a value quickly and consistently. Provide Height (if custom), Input, and Size (e.g., A4, Letter) and it returns Dimensions (mm) and Dimensions (in).
If you are comparing results across tools, keep the same units and the same level of precision. The displayed value may be rounded, so copy more decimal places when you need a tighter match.