Why is the ISO A/B/C aspect ratio always 1:1.414?

1.414 is √2. ISO 216 was designed so cutting a sheet in half along its long edge produces two sheets with the exact same aspect ratio — that's the only ratio where this works. A0 has an area of exactly 1 m²; each step halves the area.

Are pixel dimensions exact?

Pixels = mm × DPI / 25.4, rounded to the nearest integer. So A4 at 300 DPI is 2480 × 3508 px (the standard 'print-ready A4' size in Photoshop). The mm and inch values themselves come from the published standards.

What's the difference between Letter and ANSI A?

They're the same physical size (8.5 × 11″ = 215.9 × 279.4 mm). 'Letter' is the everyday name; 'ANSI A' is the same sheet as part of the ANSI engineering series (A, B, C, D, E) that doubles like ISO.

What DPI should I use?

72 for legacy web/PDF, 96 for Windows screen, 150 for draft print or large posters viewed from a distance, 300 for standard print (books, magazines, photos), 600+ for fine art or small detail. Most photo labs assume 300 DPI.

Paper Size Reference & Pixel Calculator

Convert

A complete reference for paper sizes used in printing, design and document setup. Lists every ISO 216 A, B and C size (A0–A10, B0–B10, C0–C8), all common North American sizes (Letter, Legal, Junior Legal, Tabloid, Ledger, Executive, Government, ANSI A–E), Japanese JIS-B series, photo print sizes (2R–24×36″) and standard envelopes (DL, C5, C6, #10, Monarch, Chou/Kaku). For each size you get the width × height in millimeters, inches and pixels at your chosen DPI (72/96/150/300/600 or custom), plus aspect ratio. The compare panel renders any two sizes overlaid at correct relative scale with a width/height/area ratio breakdown — great for picking print sizes, designing for fixed paper, or estimating image dimensions for a target resolution.

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Paper standardDPI presetCustom DPI

Name	Width (mm)	Height (mm)	Width (in)	Height (in)	Pixels @ DPI	Aspect
A0	841	1,189	33.11	46.811	9933 × 14043	1:1.414
A1	594	841	23.386	33.11	7016 × 9933	1:1.416
A2	420	594	16.535	23.386	4961 × 7016	1:1.414
A3	297	420	11.693	16.535	3508 × 4961	1:1.414
A4	210	297	8.268	11.693	2480 × 3508	1:1.414
A5	148	210	5.827	8.268	1748 × 2480	1:1.419
A6	105	148	4.134	5.827	1240 × 1748	1:1.41
A7	74	105	2.913	4.134	874 × 1240	1:1.419
A8	52	74	2.047	2.913	614 × 874	1:1.423
A9	37	52	1.457	2.047	437 × 614	1:1.405
A10	26	37	1.024	1.457	307 × 437	1:1.423

Compare two sizes

Size A (red)Size B (blue)

Scale B/A (W)×1.028

Scale B/A (H)×0.941

Area ratio×0.967 (-3.3%)

A4: 210 × 297 mm
Letter: 215.9 × 279.4 mm

All sizes are based on published international standards (ISO 216, ANSI Y14.1, JIS P 0138). Pixel = mm × DPI / 25.4.

How to use

Pick a paper standard (ISO A, ISO B, ISO C, US, JIS-B, Photo, Envelope) to see its sizes in the table.
Set the DPI for pixel dimensions — 72 (web), 96 (Windows screen), 150 (draft print), 300 (standard print), 600 (high-quality print) or any custom value.
Click any width, height or pixel cell to copy its value.
Use the compare panel to overlay two sizes (e.g. A4 vs Letter) and see the exact scale factors and area difference.

Frequently asked questions

Why is the ISO A/B/C aspect ratio always 1:1.414?: 1.414 is √2. ISO 216 was designed so cutting a sheet in half along its long edge produces two sheets with the exact same aspect ratio — that's the only ratio where this works. A0 has an area of exactly 1 m²; each step halves the area.
Are pixel dimensions exact?: Pixels = mm × DPI / 25.4, rounded to the nearest integer. So A4 at 300 DPI is 2480 × 3508 px (the standard 'print-ready A4' size in Photoshop). The mm and inch values themselves come from the published standards.
What's the difference between Letter and ANSI A?: They're the same physical size (8.5 × 11″ = 215.9 × 279.4 mm). 'Letter' is the everyday name; 'ANSI A' is the same sheet as part of the ANSI engineering series (A, B, C, D, E) that doubles like ISO.
What DPI should I use?: 72 for legacy web/PDF, 96 for Windows screen, 150 for draft print or large posters viewed from a distance, 300 for standard print (books, magazines, photos), 600+ for fine art or small detail. Most photo labs assume 300 DPI.