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Paper Size Reference

Compare standard paper sizes side-by-side, convert to millimetres, inches or pixels at any DPI, and learn which size fits your use case.

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Full series table

ISO A series · 11 sizes
Name mm inches px @ 300 DPI Area Aspect
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Formula

aspect ratio = long side short side = √2 ≈ 1.41421
A0
Reference sheet with area exactly 1 m² — 841 × 1189 mm
An
Obtained by folding An−1 in half across its long side
Bn
Geometric mean between An−1 and An
Cn
Geometric mean between An and Bn — sized to envelope An
A4 A4 A3 = two A4s sharing a long edge fold here →
Folding any A-size sheet across the long edge produces two copies of the next smaller A size — because every A-series sheet shares the 1 : √2 aspect ratio, the property is preserved at every step.
Worked example — A4 from A0
  1. A0 area = 1 m² and ratio √2 → A0 = 841 × 1189 mm
  2. A1 = A0 halved on long side → 594 × 841 mm
  3. A2 = A1 halved → 420 × 594 mm
  4. A3 = A2 halved → 297 × 420 mm
  5. A4 = A3 halved → 210 × 297 mm
  6. A4 aspect = 297 / 210 = 1.4143 ≈ √2

Pixel dimensions come straight from the inch size: px = inches × DPI. A4 at 300 DPI is 8.27 × 300 ≈ 2480 px wide and 11.69 × 300 ≈ 3508 px tall. US Loose sizes (Letter, Legal, Tabloid) predate ISO and do not share a constant aspect ratio, which is why A4 ↔ Letter scaling is never a clean operation.

Examples

How It Works

Paper sizes come from two dominant systems. The ISO 216 family (used by most of the world) starts from A0 at exactly 1 m² and halves the long side at each step, so A1 is half of A0, A2 is half of A1, and so on. Every size shares the same aspect ratio of 1 : √2 ≈ 1.414, which is why folding any A-size sheet in half gives you the next size down without losing that ratio.

The B and C series follow the same √2 rule but start from different reference areas — B sizes slot geometrically between two adjacent A sizes, and C sizes are sized to hold an A sheet as an envelope (C4 fits A4 flat, C5 fits A4 folded once, C6 fits A4 folded twice).

The US Loose system (Letter, Legal, Tabloid, Ledger) is based on historical imperial fractions and does not share a constant aspect ratio — that's why scaling a Letter document onto Legal or A4 introduces white bands or crops. The ANSI series (A–E) is a US engineering-drawing family that does halve like ISO, but with two alternating aspect ratios.

When you need pixel dimensions, multiply the size in inches by your target DPI: A4 at 300 DPI is 2480 × 3508 px, which is the standard for print-ready artwork. Screen mockups typically use 72 DPI, inkjet prints 150 DPI, and commercial litho / photo printing 300 DPI or higher.

Tips & Best Practices

When designing for print, work in millimetres with a 3 mm bleed past the trim edge — art that ends exactly at the edge risks thin white slivers after cutting.
Scan or export at 300 DPI for commercial print, 150 DPI for home inkjet, and 72 DPI for web. Going higher wastes file size without a visible quality gain.
Scaling A4 → Letter (or vice versa) is not a clean operation: the aspect ratios differ (1.414 vs 1.294), so choose fit (white bands) or fill (crop) intentionally.
Envelope rule of thumb: Cn fits An flat, and the next size up (Cn-1) fits it folded. So a C5 envelope takes an A4 folded once.
If you fold any ISO A sheet in half across the long side, the two halves are the next size down — A4 folded gives two A5s — because every A size shares the 1 : √2 ratio.

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Frequently Asked Questions

What is the difference between A4 and US Letter?

A4 is 210 × 297 mm (8.27 × 11.69 in); Letter is 216 × 279 mm (8.5 × 11 in). A4 is slightly narrower and noticeably taller, and the two have different aspect ratios (1.414 vs 1.294), so one cannot be scaled perfectly onto the other — you either lose content or gain white borders.

The √2 aspect ratio is the only ratio preserved when you fold a sheet in half. That property means every A size is a clean scale of every other A size, so a two-up A5 layout prints perfectly onto A4 without empty strips or cropping, and A3 photocopied down to A4 keeps the same proportions. This also makes A-series the natural choice for paper-saving duplex and booklet printing.

Multiply the size in inches by your target DPI. A4 (8.27 × 11.69 in) at 300 DPI becomes 8.27 × 300 ≈ 2480 px wide and 11.69 × 300 ≈ 3508 px tall. This tool does the rounding for you at 72, 150, 300, and 600 DPI.

72 DPI for screen-only artwork, 150 DPI for home or office inkjet prints where you look at the page from a normal reading distance, 300 DPI for commercial offset printing and magazine-quality work, and 600 DPI for fine-art reproductions or very small text. Higher than 600 DPI rarely produces a visible improvement and costs a lot of file size.

DL (110 × 220 mm) takes an A4 sheet folded into thirds and is the European business standard. C5 (162 × 229 mm) takes an A4 folded once (in half). C4 (229 × 324 mm) takes an A4 flat without folding.

No. ISO B sizes are the geometric mean of two adjacent A sizes (B4 = 250 × 353 mm). Japanese JIS B sizes are the arithmetic mean and are slightly larger (B4 JIS = 257 × 364 mm). If you are working with Japanese books or stationery, use the JIS values.

ANSI/ASME Y14.1 is a US engineering-drawing family that doubles Letter: ANSI A = Letter (8.5 × 11 in), ANSI B = Tabloid (11 × 17 in), ANSI C = 17 × 22 in, ANSI D = 22 × 34 in, ANSI E = 34 × 44 in. Unlike ISO, ANSI alternates between two aspect ratios as you step up.