Paper Size Converter

Paper Size Converter — ISO and US Dimensions in Millimeters and Inches: The ISO 216 standard defines three paper series — A for general documents, B for posters and enlarged formats, and C for envelopes — each maintaining a consistent aspect ratio of 1:√2. Starting from a base size at number 0, every subsequent size is produced by halving the longer dimension. This free converter computes the exact dimensions and area for any size in these series, running instantly offline with no signup required ever and returning results in seconds.

The A series begins at A0, which measures 841 × 1189 mm and covers exactly one square meter. Halving A0 gives A1, halving A1 gives A2, and so on down to A5 (the popular half-letter size) and beyond. A4 at 210 × 297 mm is the global standard for business documents, used across Europe, Asia, and most of the world.

The B series fills the gaps between consecutive A sizes and is commonly used for posters, books, and maps. B5 is a popular notebook size in the US, while B2 is standard for medium-format posters. The C series is designed so each envelope comfortably holds the corresponding A sheet — a C4 envelope fits an unfolded A4 page perfectly.

US Letter (8.5 × 11 in, or 215.9 × 279.4 mm) is close to but not identical to A4. Letter is wider by about 6 mm and shorter by about 7 mm, meaning documents formatted for one system will have slightly different margins on the other. Legal paper (8.5 × 14 in) and Tabloid (11 × 17 in) have no direct ISO equivalent. The converter shows both metric and imperial dimensions for every result.

All calculations run locally in your browser using pure arithmetic — no data leaves your device, no accounts are needed, and no server calls are made. Whether you are a New York print production manager scheduling a $50,000 offset run, a Chicago designer preparing a portfolio on 09/15/2026, or a Seattle student formatting a thesis, this converter eliminates guesswork about paper dimensions across all international and US standards.