Paper Size Converter

How to use Paper Size Converter

1. Pick a size from the list.
2. Read its dimensions in millimetres, centimetres and inches.
3. Compare against the other sizes in the table to find the nearest equivalent.
4. ISO sizes are defined in millimetres; inch values are rounded conversions.
5. Every A and B size shares the 1:√2 ratio, so folding one in half gives the next size down.
6. A4 at 300 dpi is 2480 × 3508 pixels; at 150 dpi it is 1240 × 1754.

Why the A series halves so neatly

Every A size has the same aspect ratio, 1:√2, which is the only ratio that keeps its proportions when you fold it in half. So A4 is exactly half of A3, which is half of A2, and A0 is defined as the sheet of that ratio with an area of exactly one square metre. That is what makes scaling trivial: printing two A4 pages onto one A3 sheet, or reducing A3 to A4 at 71%, loses no margin and distorts nothing. The B series fills the gaps between A sizes using the same ratio, and is mostly used for posters, books and envelopes.

A4 and Letter are close enough to cause trouble

A4 is 210 × 297 mm; US Letter is 216 × 279 mm. Letter is 6 mm wider and 18 mm shorter — near enough that a document looks fine on screen and wrong on paper. Printing A4 content on Letter clips the bottom or shrinks the page; printing Letter on A4 leaves an odd band at the foot. If a document crosses the Atlantic, either set generous margins that survive both or export a PDF with the target size chosen deliberately. North America, and parts of Central and South America and the Philippines, use Letter; almost everywhere else uses A4.

Sizes worth memorising

A4 is 210 × 297 mm, or 8.27 × 11.69 inches — a page of writing. A3 is double it, for posters and spreads. A5 is half, for notebooks and flyers. A6 is a postcard. A0 is the square-metre poster used for academic conferences. US Letter is 8.5 × 11 inches, Legal is 8.5 × 14, and Tabloid is 11 × 17, the Letter equivalent of A3.

Millimetres, inches and the resolution question

Paper sizes are defined in millimetres and the inch figures are conversions, which is why A4 in inches is an awkward 8.27 × 11.69 rather than a round number. For print work you also need a resolution: A4 at 300 dpi, the standard for commercial printing, is 2,480 × 3,508 pixels; at 150 dpi for office printing it is half that. Designing to pixel dimensions without fixing the dpi is how artwork ends up the wrong physical size.