What are the dimensions of A4 paper?

A4 measures 210 by 297 millimetres, which is 21.0 by 29.7 centimetres or about 8.27 by 11.69 inches. It is the standard office and letter-equivalent size across most of the world outside North America.

Why is the aspect ratio of ISO paper one to the square root of two?

The ratio of 1 to 1.414 is special because halving the long side keeps the same proportions. That means cutting or folding any A size in half produces two sheets of the next smaller A size with identical shape, which makes scaling between sizes lossless.

A0 measures 841 by 1189 millimetres and has an area of almost exactly one square metre. Every smaller A size is defined by repeatedly halving the long dimension, so A1 is half of A0, A2 is half of A1, and so on.

What is the difference between the A and B series?

Both share the 1 to root-two ratio, but B sizes sit between consecutive A sizes. B0 is one metre wide and is larger than A0, so the B series is used for posters, books, passports, and envelopes that need to hold an A size with margin.

Why do the dimensions not always halve to a whole number?

ISO 216 defines each size by halving the previous one and then rounding down to the nearest whole millimetre. That rounding is why A5 is 148 by 210 rather than exactly 148.5, and the table reproduces the official rounded values.

What is the ISO Paper Sizes Reference?

Full ISO 216 A-series and B-series paper size table with width and height in millimetres, centimetres, and inches. Switch series and units instantly, from A0 down to A10 and B0 to B10. It runs free in your browser on Gera Tools, with nothing uploaded.

ISO Paper Sizes Reference

Name: ISO Paper Sizes Reference
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

Get one useful tool a week

Like this tool? Enter your email and we'll send you one genuinely useful Gera tool a week — plus a link to come back to this one. No spam, one-click unsubscribe any time.

The ISO 216 standard defines the A and B paper series used almost everywhere outside North America. This reference lists every size from the wall-sized A0 down to the tiny A10, plus the full B series, in millimetres, centimetres, and inches.

The elegant maths behind the ISO series

ISO paper is built on one rule: every sheet has the aspect ratio 1 : √2 ≈ 1 : 1.414. This is the only ratio where folding a sheet in half across its long edge gives a smaller sheet of exactly the same proportions. The consequence is that two A5 sheets make an A4, two A4 sheets make an A3, and so on — with no wasted paper and no distortion when you scale a document up or down between any two sizes in the series.

The series is anchored by A0 = 841 × 1189 mm, whose area is almost exactly one square metre. Each next size halves the long dimension and rounds down to the whole millimetre, which is why A4 is 210 × 297 rather than a tidy fraction. The B series starts at B0 = 1000 × 1414 mm and fills the gaps between A sizes.

The A series: common uses by size

Size	Dimensions (mm)	Typical use
A0	841 × 1189	Engineering drawings, large posters
A1	594 × 841	Architectural plans, exhibition posters
A2	420 × 594	Large-format posters, flip-chart pads
A3	297 × 420	Tabloid-style layouts, spreadsheet printing, manga
A4	210 × 297	Office documents, magazines, letters worldwide
A5	148 × 210	Notepads, booklets, flyers
A6	105 × 148	Postcards, pocket notebooks
A7	74 × 105	Small notebooks, flashcards
A8–A10	52 × 74 down to 26 × 37	Tiny labels, business card variants

The B series and its role

The B series uses the same 1 : √2 ratio but is anchored at B0 = 1000 × 1414 mm, making each B size slightly larger than the corresponding A size. B sizes fill the gaps: B4 is between A3 and A4, B5 is between A4 and A5.

Common B-series uses:

B5 (176 × 250 mm) — popular book format; fits between A4 and A5
B4 (250 × 353 mm) — newspapers, some tablet covers
B0 — large-format printing and signage

Practical scaling and printing tips

To print an A3 document onto two A4 sheets, tile it — A3 is exactly two A4s side by side, so the halves line up without gaps. To shrink an A4 page to A5, scale to about 71% (which is 1 ÷ √2). To enlarge A5 to A4, scale to 141%. These percentages are exact because of the 1 : √2 ratio.

When setting up documents in software, always specify sizes in millimetres — the metric values are the official definition. The inch figures in this table are rounded approximations (based on 1 inch = 25.4 mm) and are slightly less precise, though useful for configuring US-based printing software that requires inch inputs.