A4 vs US Letter
A4 is 210 × 297 mm; US Letter is 215.9 × 279.4 mm. Letter is 6 mm wider and 18 mm shorter — small numbers, big printing headaches.
Side by side
| A4 | US Letter | |
|---|---|---|
| Width | 210 mm (8.27") | 215.9 mm (8.5") |
| Height | 297 mm (11.69") | 279.4 mm (11") |
| Aspect ratio | 1 : 1.414 (√2) | 1 : 1.294 |
| Standard | ISO 216 | ANSI |
Why documents break between them
Because the shapes differ, a page designed for one size doesn't fit the other: A4 content is too tall for Letter (bottom gets cut), Letter content is too wide for A4 (side margins shrink). The A-series' √2 ratio also means A4 halves perfectly into A5 — Letter has no such system.
The fix is simple once you know it: in the print dialog, set the actual paper in your tray and enable "scale to fit" (or "fit to printable area"). For PDFs you share internationally, A4 with generous bottom margins survives both worlds best.
Frequently asked questions
Which is bigger, A4 or Letter?
Neither, exactly: Letter is 6 mm wider, A4 is 18 mm taller. Letter has slightly less area.
Why does my A4 document print wrong on Letter paper?
A4 is taller than Letter, so the bottom gets cut off unless the printer scales it. Enable "scale to fit" in the print dialog.
What is the ratio of A4 paper?
1 : √2 (about 1 : 1.414) — the ISO ratio that lets each A-size fold exactly in half into the next.