ISO Paper Size Calculator

ISO 216 defines the A, B, and C paper series used in most countries outside North America. Every size keeps the same width-to-height ratio: √2 (about 1.414). That ratio is deliberate — when you fold a sheet in half parallel to the short edge, the two halves have the same proportions as the parent sheet. A3 folded becomes A4; A4 folded becomes A5. Designers can scale artwork between sizes without cropping or stretching.

The A series is for general office and document printing. A4 (210 × 297 mm) is the global default for letters, invoices, and school handouts. The B series sits between A steps — B4 is between A4 and A3 — and appears in posters, books, and some envelope formats. The C series is sized to fit A sheets inside envelopes: C4 holds a flat A4 sheet without folding.

Area doubles or halves cleanly as you step sizes. A0 has exactly one square meter of area (841 × 1189 mm). Each step down (A0 → A1 → A2…) halves area. That makes paper weight calculations simple: 80 g/m² A4 weighs half as much per sheet as 80 g/m² A3 because A4 is half the area.

Worked example with the default fields: A series, size 4 (A4). Dimensions are 210 × 297 mm — short edge × long edge. In inches that is 8.27 × 11.69 in. Area is 0.062 m², shown as 620 cm² in the results. Compare to US Letter at 8.5 × 11 in (216 × 279 mm): A4 is slightly narrower and taller, which breaks layouts when you assume they are interchangeable.

B4 at 250 × 353 mm is a common European tabloid substitute. C5 envelopes fit A5 sheets folded once. Printers and copy shops in the US may stock A4 for international clients even when Letter is the domestic default — always confirm availability before designing a run.

Common mistakes include confusing A4 with US Letter in PDF export presets, designing full-bleed artwork at trim size without adding bleed (see the bleed calculator), and assuming landscape versus portrait swaps the ISO number — A4 landscape is still A4, just oriented with the long edge horizontal.

Size numbers run from 0 (largest) to 10 (smallest) within each series. Not every print vendor stocks A1 or B1 on demand; digital presses often cap at SRA3 or 13 × 19 in sheets. Use this lookup before specifying paper in RFQs.

Limits: this tool returns nominal ISO dimensions. Actual sheets may vary ±1–2 mm per manufacturer tolerance. US architectural sizes (ARCH A, B, C) and Japanese B variants (JIS) are different standards — do not mix them with ISO B without checking tables.