ISO 216 specifies trimmed writing-paper sizes in the A and B series. PaperSize’s finite launch catalog uses three familiar A entities: A3 at 297 × 420 mm, A4 at 210 × 297 mm, and A5 at 148 × 210 mm. Those integer millimetres are the canonical inputs. Centimetres and inches are derived views, not replacements for the standard values.
Keep the published millimetre dimensions intact
A3 is 297 × 420 mm, A4 is 210 × 297 mm, and A5 is 148 × 210 mm in portrait order. Landscape reverses the same pair; it does not create a different paper entity. Converting A4 to inches gives about 8.2677 × 11.6929, but rounding those figures and converting back must not overwrite 210 × 297 mm. PaperSize always recalculates from the canonical base.
The family preserves a near-square-root-of-two proportion
The A-series design lets adjacent sizes retain the same overall shape when one sheet is divided across its longer side. In practice the published integer millimetres include necessary rounding, so PaperSize uses the stated dimensions rather than regenerating every size from an ideal ratio. A3, A4, and A5 are finite named standards, not arbitrary width-and-height combinations.
Letter and Legal begin from inches, not ISO millimetres
North American Letter is 8.5 × 11 inches and Legal is 8.5 × 14 inches. Using the exact 25.4 mm per inch conversion gives 215.9 × 279.4 mm and 215.9 × 355.6 mm. PaperSize labels those metric values as derived and does not round them to a new canonical size. A4 and Letter are close enough to look interchangeable, yet their widths, heights, and proportions differ.