A4 Paper Size: Dimensions in Inches, cm, mm and Pixels

A4 dimensions in every unit

ISO 216 defines A4 in whole millimeters. Every other figure below is a conversion, rounded to the precision you would actually use.

The diagonal of an A4 sheet is 363.7 mm (14.32 in), which explains why a 14-inch laptop is close to the size of a sheet of paper. The perimeter is 1,014 mm.

Why A4 is 210 × 297 mm

The numbers look arbitrary, but they come from two simple rules that a German engineer, Walter Porstmann, set out in the DIN 476 standard in 1922. ISO adopted the same system in 1975 as ISO 216.

1. The sides have a ratio of 1:√2. When you cut or fold a sheet in half across its long side, the two halves have exactly the same proportions as the original. Nothing else does this.
2. A0 has an area of one square meter. Solving for a 1 m² rectangle with a 1:√2 ratio gives 841 × 1189 mm.
3. Each step down halves the area. A1 is half of A0, A2 is half of A1, and so on. A4 is A0 halved four times, so it has 1/16 of a square meter (before rounding).

Each size is rounded down to the nearest millimeter, which is why A4 is 210 × 297 mm rather than 210.2 × 297.3 mm.

The practical payoff is that you can scale between sizes without cropping or leaving white space. Enlarge an A4 page to A3 on a photocopier at 141% (√2), or shrink two A4 pages onto one A4 sheet at 71%, and the layout fits exactly. Printers and designers rely on this every day.

A4 compared with the other A sizes

A4 is the middle of the series in daily use. A3 is the larger format for posters and drawings, and A5 is the notebook and flyer size. Every row below is half the area of the one above it.

A3 297 × 420 mmA4 210 × 297 mmA5 148 × 210 mmA6 105 × 148 mm

For notebooks in A5 and the larger B5 format, see the A5 notebook size guide and the overview of notebook sizes. The full set of A, B and C series is covered in the paper sizes guide.

A4 vs US Letter

The United States and Canada use Letter (8.5 × 11 in) instead of A4, and Mexico, the Philippines and parts of Latin America use both. The two look almost identical on a desk, but the difference shows up the moment you print a document made for the other size.

A4 8.27 × 11.69 inLetter 8.5 × 11 in

Printing A4 documents on Letter paper (and the reverse)

• A4 file on Letter paper: the bottom 17 mm of the page has nowhere to go. Footers and page numbers are the usual casualties. Choose "Fit to printable area" or "Scale to fit" (about 94%) in the print dialog.
• Letter file on A4 paper: the page is 6 mm too wide, so text set close to the side margins can clip. Scaling to about 97% fixes it, and you will see a slightly larger bottom margin.
• Documents for both markets: set side margins of at least 20 mm and keep footers more than 25 mm from the bottom edge. The same layout then prints cleanly on either paper.

A4 size in pixels

A sheet of paper has no pixel size of its own. The pixel count depends on the resolution, measured in dots per inch (DPI). Multiply 8.27 × 11.69 in by the DPI you need.

For landscape orientation, swap the two numbers. If you design an A4 flyer for a commercial printer, add a 3 mm bleed on every side. The artwork then becomes 216 × 303 mm, or 2551 × 3579 px at 300 DPI.

Folding, filing and posting A4

A4 paper is the reference for a whole family of envelopes, binders and filing products.

• Hole punching: the ISO 838 two-hole pattern puts 6 mm holes 80 mm apart and 12 mm from the edge. Standard A4 ring binders and lever-arch files use it.
• Sheet protectors and folders sold as "A4" are cut a few millimeters larger than the paper. Letter-size protectors are 18 mm too short, so an A4 sheet sticks out of the top.
• Thickness: 80 gsm copy paper is about 0.1 mm thick, so a 500-sheet ream stands roughly 50 mm tall and weighs about 2.5 kg.

For every envelope format, including US commercial sizes, see the envelope size chart.

Common A4 settings in software

• Microsoft Word and Google Docs: the page size is called "A4" in Page Setup. Docs created in the US default to Letter, so check this setting before you send a CV or form to someone outside North America.
• CSS for print: @page { size: A4; } sets the page to 210 × 297 mm. Use mm units for margins so the layout matches the paper.
• Design apps: Photoshop, Illustrator, Canva and Figma all include A4 presets. In Photoshop, choose 300 pixels per inch for print work.

Frequently asked questions