International Paper Sizes: Dimensions, Formats, and Standards

ISO Paper Sizes: The Standard and Its Logic

ISO 216 sets the metric A and B series, and with ISO 269 it sets the C series used for envelopes. Sizes in a series share one proportion, 1 to the square root of 2, so cutting a sheet in half across its longer side gives the next size down with the shape unchanged. That is why a page scales between A3, A4 and A5 with nothing cropped and no margin added, and why a sheet folds cleanly into the next size. It is the working standard in more than 100 countries.

How the A Series Is Defined

A0 has an area of one square metre and a width to height ratio of 1 to 1.4142. Each smaller size is the one above it cut in half parallel to the shorter side, and the result is rounded to the nearest millimetre. That rounding is why A4 is a clean 210 by 297 mm rather than an exact irrational figure.

The B and C Series

The B series fills the gaps between A sizes. Each B size is the geometric mean of the A size with the same number and the A size above it, so B4 sits between A4 and A3. The C series does the same between the A and B series and is sized for envelopes: a C4 envelope holds an unfolded A4 sheet, a C5 holds it folded once, and a C6 holds it folded twice.

RA and SRA Untrimmed Sizes

Commercial printing starts from oversized sheets defined by ISO 217, the RA and SRA formats. They run a little larger than the matching A size to leave room for ink bleed and trimming, so an SRA3 press sheet is cut down to A3 once printed.

Scaling Between Sizes

Because the proportion is fixed, one magnification figure carries through the series. Reducing A3 to A4 needs 71 percent, the same figure that takes A4 to A5 or A5 to A6. Enlarging runs the other way at 141 percent. Print dialogs list these as fit-to-page presets. The ISO 216 standard page has the full scale-factor table.

US and ANSI Paper Sizes

The United States and Canada work in inch sizes set by trade custom rather than a single rule. Letter, Legal and Tabloid cover daily use. The ANSI/ASME Y14.1 standard adds a technical-drawing series from ANSI A to ANSI E, and the architectural Arch A to Arch E series runs alongside it. Because these sizes do not share one proportion, a Letter page does not scale onto A4 without a crop or a border.

Standard Sizes and Trade Conventions

A standard paper size is one written into a published standard, not one that shops happen to stock. The test is whether two sheets of the same name from different mills line up. ISO and ANSI sizes do, within a stated tolerance. Book trims, photo prints and newspaper formats run on trade convention, so their figures drift a millimetre or two between suppliers. Each page here names the rule that governs the size it covers.

Portrait and Landscape

The same sheet is portrait when its shorter sides are at the top and bottom, and landscape when its longer sides are. The measurements do not change, only the orientation. Size tables here quote width before height so the reading direction is clear.

Weight, Whiteness and Shade

Beyond its dimensions, paper is described by grammage in grams per square metre, which sets how heavy and stiff a sheet feels, and by separate whiteness, brightness and shade measures for how the white is tinted. The paper weight and GSM page covers the grammage conversions and what each figure means in practice.

Paper Sizes Before ISO 216

Many systems were in use before the metric standard spread. British Imperial names such as Foolscap, Crown, Demy and Royal were common across the Commonwealth, Japan kept its own traditional sizes, and mainland Europe had a patchwork of local formats. Several of those names are still used for book trims today.

About the Figures on This Site

Each size lists its dimensions in millimetres, centimetres, inches, points and pixels, with the governing standard named and a verification date. For the wider history and the underlying geometry, the Wikipedia article on international standard paper sizes is a solid reference.