Paper looks like the most boring object in the office until you try to print a US document on a European printer. Two parallel systems govern the world: the ISO 216 A-series used almost everywhere, and the US Letter family used across North America. Knowing both — and the geometry behind them — saves a surprising amount of frustration.
The A-Series at a Glance
| Size | Millimetres | Inches | Typical use |
|---|---|---|---|
| A0 | 841 × 1189 | 33.1 × 46.8 | Posters, technical drawings |
| A1 | 594 × 841 | 23.4 × 33.1 | Large posters, presentations |
| A2 | 420 × 594 | 16.5 × 23.4 | Medium posters, art prints |
| A3 | 297 × 420 | 11.7 × 16.5 | Spreadsheets, charts |
| A4 | 210 × 297 | 8.3 × 11.7 | Standard office paper |
| A5 | 148 × 210 | 5.8 × 8.3 | Notebooks, flyers |
US Letter, Legal and Tabloid
North America uses an imperial-based system standardised by ANSI. US Letter (8.5 × 11 in) is the everyday office sheet — closest cousin to A4. US Legal (8.5 × 14 in) is the same width but taller, traditionally used for contracts and court filings. Tabloid or Ledger (11 × 17 in) is roughly the size of A3 and is used for spreadsheets, blueprints, and newspaper proofs. The ANSI series doubles like the A-series, but because the starting ratio is not √2, alternate sizes have different aspect ratios, making scaling less elegant.
The √2 Trick
The genius of ISO 216 is the aspect ratio of 1:√2 (≈ 1:1.414). Cut any A-size sheet in half across the long edge and you get two sheets of the next smaller A-size with the same aspect ratio. That is why two A5 pages fit perfectly on one A4, four A6 pages on an A4, and 16 A4 pages tile precisely onto an A0 poster. Printers, photocopiers, envelopes, and binders are all designed around this property, so scaling artwork between sizes never distorts.
Practical Scaling and Printing Tips
That √2 ratio turns awkward print jobs into one-number settings. Keep these handy:
- Enlarge one step up: set the copier to 141% (√2) to go A4 → A3 or A5 → A4 with no cropping.
- Shrink one step down: use 71% (1/√2) for A3 → A4 or A4 → A5.
- Two steps double or halve the scale: A4 → A2 is 200%, A4 → A6 is 50%.
- Booklets: two A5 pages sit side by side on one A4 sheet, so “2-up” printing and saddle-stitch booklets fall out naturally.
- Mind the margins: most printers can't reach the paper edge, so true edge-to-edge (“full bleed”) artwork needs a slightly larger sheet trimmed down.
- Letter vs A4 gotcha: a document laid out for A4 may clip or shift when printed on US Letter, since Letter is wider but shorter — always set the correct paper size before printing.
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