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Paper Size Reference

Pick a paper size to instantly see its width and height in millimetres, centimetres, inches and web/print pixels (96 dpi & 300 dpi), with a side-by-side visual against A4. Covers ISO 216 A and B series, C-series envelopes, North American Letter / Legal / Tabloid, plus credit card, Octopus and business-card sizes.

Relative size (vs A4)

A4
Millimetres (mm)
—
Centimetres (cm)
—
Inches (in)
—
Pixels @ 96 dpi (web)
—
Pixels @ 300 dpi (print)
—
Aspect ratio
—

ISO 216 (A / B / C series) uses a √2 aspect ratio: folding the long edge in half always yields the next size down. US Letter and Legal sit outside ISO.

Formula

A0 = 841 × 1189 mm; A(n+1) = half of A(n) along the long edge; aspect ratio width : height = 1 : √2

Frequently asked

What is the pixel size of A4 paper?

A4 measures 210 × 297 mm. In pixels this depends on DPI: about 794 × 1123 px at 96 dpi (web), 2480 × 3508 px at 300 dpi (print) and 4960 × 7016 px at 600 dpi. Photoshop and Illustrator default to 300 dpi when creating an A4 document.

What is the difference between A4 and US Letter?

A4 (210 × 297 mm) is the ISO 216 international standard used in Hong Kong, Europe, Asia and Australia. US Letter (8.5 × 11", 215.9 × 279.4 mm) is the ANSI standard — slightly wider but shorter. Printing an A4 PDF on Letter clips roughly 18 mm off the bottom (or vice versa), so it is worth reformatting before sending to a US recipient.

What size should a business card be?

In Hong Kong and Japan, 91 × 55 mm is the most common size. Europe often uses ISO 7810 ID-1 (85.60 × 53.98 mm, the credit-card size). The US standard is 89 × 51 mm (3.5 × 2"). Design with ±3 mm bleed, keep important content at least 5 mm from the trim, and export at 300 dpi CMYK.

Why is the A-series aspect ratio √2?

When the aspect ratio equals √2, folding the long edge in half produces a new sheet with the exact same ratio. That means two A4 sheets tile into an A3, two A3s into an A2, and so on — perfect for scaling and zero waste. German engineer Walter Porstmann codified this in DIN 476 in 1922, which later became ISO 216.

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