A4 Size in Pixels, cm and Inches

How the Paper Sizes works

Two paper systems are in everyday use, and they do not share a single size. The ISO 216 A-series is standard almost everywhere. North American sizes are used in the US, Canada and Mexico. Anyone exporting a PDF across that line needs both.

The A4 size in pixels, and why it depends on DPI

Paper has a physical size but no pixel size of its own. The pixel count depends on how many pixels you print per inch, so the formula is

pixels = millimetres ÷ 25.4 × DPI

An inch is exactly 25.4 mm, so A4's 210 mm width is 8.27 inches.

Example: A4 at 300 DPI. 210 ÷ 25.4 × 300 = 2480 pixels wide, and 297 ÷ 25.4 × 300 = 3508 pixels tall. That is the canvas for a print-quality A4 page.

Example: Letter at 150 DPI. 8.5 × 150 = 1275 by 11 × 150 = 1650 pixels.

Use 300 for anything held in the hand and 150 for posters seen from a metre or two. PDF software reports A4 as 595 × 842 because it measures in points of 1/72 inch.

How the A-series is built

A0 is defined as one square metre with sides in the ratio 1 to √2, which rounds to 841 by 1189 mm. Each smaller size halves the longer side: A1 is half an A0, A4 is a sixteenth, and A5 is half an A4. Because √2 survives halving, every A size has the same proportions. A4 enlarges to A3 at 141 % or shrinks to A5 at 71 % with nothing cropped, the photocopier presets.

B sizes sit between A sizes. C envelopes fit the A-series: an A4 sheet slides flat into a C4, folded once into a C5, and folded in three into a DL.

North American sizes come from inches, not a ratio. Letter is 8.5 by 11 inches, Legal 8.5 by 14, and Tabloid or Ledger 11 by 17. Letter and A4 are close but not interchangeable: Letter is 6 mm wider and 18 mm shorter.

How many pixels for each paper size at 300 DPI?

Common paper and envelope sizes in millimetres, inches and pixels at 300 DPI, portrait

Reading the result

• Millimetres is the defining size for ISO paper and an exact conversion for inch-based sizes.
• Centimetres and Inches are the same size to two decimals. For Letter and Legal the inches are the exact figure.
• Pixels at … DPI rounds each side to the nearest whole pixel at the density you entered, in the orientation you chose.
• Aspect ratio shows the long side divided by the short. Every A and B size shows 1 : 1.414. Letter shows 1 : 1.294 and a 6 × 4 photo 1 : 1.500, which is why a camera image needs cropping to fit an A4 page.

Tips and pitfalls

• Check the printer default. Word and Google Docs install with Letter in the US and A4 elsewhere. A PDF made on the wrong one prints with a gap at the bottom or the footer cut off.
• Add bleed for commercial print. Printers usually want 3 mm (1/8 inch in the US) past each edge, so an A4 flyer at 300 DPI becomes 2551 by 3579 pixels.
• DPI in file metadata changes nothing. Setting a 1200-pixel image to 300 DPI only means it prints 4 inches wide. Resample if you need more pixels.

To go from pixels to print size, use the print size calculator or pixels to inches. The image DPI tool reads and changes the density stored in a file, and the image resizer sets the exact pixel dimensions from the chart.

Sources: ISO 216.

Checked against: ISO 216: A4 = 210 × 297 mm

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