A Paper Sizes (A0–A10) in mm and inches

Understanding the A paper size chart — concept and principle

The A series of paper sizes, defined in the international standard ISO 216, is used for letters, documents, posters and drawings in almost every country outside North America. This chart gives the exact dimensions of A0 to A10 in millimetres and inches, so you can set up a print layout, choose a frame or envelope, or compare a size with US Letter.

A4 (gold) is A0 halved four times, which is why 16 sheets of A4 make one A0.

How it is calculated

The chart is a lookup table taken from ISO 216; inches are the millimetre values divided by 25.4 (1 inch = 25.4 mm exactly), rounded to two decimals.

A0 = 841 × 1189 mm, area very close to 1 m².
Each next size is made by halving the longer side: A(n+1) short side = A(n) long side ÷ 2, rounded down to the whole millimetre, and the old short side becomes the new long side.
All sizes have a side ratio of about 1 : √2 (1 : 1.414).

The principle

The √2 ratio is the only ratio that survives folding in half: if a sheet is 1 by √2, half of it is √2/2 by 1, which is again 1 : √2. This means an A3 sheet folds into two A4 sheets of exactly the same shape, and a photocopier can enlarge A4 to A3 at 141% or reduce A3 to A4 at 71% without cropping or white margins. Fixing A0 at 1 m² also makes paper weight easy: a 80 g/m² A4 sheet, 1/16 of A0, weighs about 5 g.

Worked example

Start from A0 = 841 × 1189 mm.
A1 = 594 × 841 (1189 ÷ 2 = 594.5, rounded down to 594).
A2 = 420 × 594, A3 = 297 × 420, A4 = 210 × 297 mm.
In inches: 210 ÷ 25.4 = 8.27 and 297 ÷ 25.4 = 11.69, so A4 = 8.27 × 11.69 in.

How to read the result

Every step down halves the area: A4 is half of A3, a quarter of A2 and 1/16 of A0. A4 is the standard office sheet; A5 suits notebooks and flyers; A3 is used for spreads and small posters; A1 and A0 for posters and technical drawings. The US Letter size is 8.5 × 11 in (215.9 × 279.4 mm), slightly wider and shorter than A4, so documents moved between them may reflow or lose margins.

Common mistakes

Assuming A4 and US Letter are interchangeable in print settings.
Forgetting printers' bleed and non-printable margins when designing to the exact sheet size.
Confusing the A series with the B series, which is larger at each number (B4 is bigger than A4).
Rounding inch values and then converting back, which creates small errors.

Keep in mind: Listed sizes are nominal; the standard allows small manufacturing tolerances, and print shops may add bleed. Check the printer's specification for professional jobs.

Frequently asked questions

How many A4 sheets make an A0?

Sixteen, because each size step halves the area and A4 is four steps below A0.

What zoom turns A4 into A3?

About 141% (√2); A3 to A4 is about 71%.

Why is A0 not exactly 1 m²?

Its sides are rounded to whole millimetres, so 841 × 1189 mm = 0.99995 m².

Sources: ISO 216:2007, Writing paper and certain classes of printed matter — Trimmed sizes — A and B series

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