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Paper size refers to the dimensional range compatible with folding and binding equipment. Such equipment is typically rated for a specified maximum and minimum paper size, defined in accordance with standardized paper dimensions. Paper sheets falling outside this operational range cannot be processed reliably by the machinery.
The A4 format is defined under ISO 216-the international standard for paper sizes-and is the most widely adopted paper size globally. China formally adopts ISO 216, ensuring full alignment with international specifications.
Standard ISO 216 Paper Dimensions (in millimeters):
• A0: 841 × 1189
• A1: 594 × 841
• A2: 420 × 594
• A3: 297 × 420
• A4: 210 × 297
Note: Dimensions are expressed as width × height (mm), consistent with ISO conventions.
Dimensional Derivation Principle
All A-series paper sizes share a common aspect ratio of √2:1 and are derived recursively: each successive size (e.g., A1 → A2) is obtained by halving the preceding size along its longer side. Thus, A4 is generated by halving A3 along its length, A3 from A2, and so forth-ultimately tracing back to the base A0 sheet (area = 1 m²).
Practical Utility
A4 remains the de facto standard for everyday office, academic, and administrative documentation. Memorizing its dimensions (210 mm × 297 mm) enables rapid mental derivation of other A-series sizes, given their mathematically consistent scaling.
Digital Representation: Pixel Dimensions at Common Resolutions
Based on the physical A4 dimensions (210 mm × 297 mm) and the conversion factor of 1 inch = 25.4 mm, the corresponding pixel dimensions at standard print resolutions are as follows:
• 72 ppi: 595 × 842 pixels
• 120 ppi: 991 × 1404 pixels
• 150 ppi: 1239 × 1754 pixels
• 300 ppi: 2479 × 3508 pixels
Note: Pixel dimensions are presented as width × height (consistent with raster image conventions); values have been recalculated for accuracy and rounded to the nearest integer.
