A4 to Letter Paper Size

A4 measures 210 x 297 mm (8.27 x 11.69 inches). US Letter measures 8.5 x 11 inches (215.9 x 279.4 mm). The visual difference is small enough that most people do not notice when comparing the two side by side, but the practical difference matters constantly: a UK CV designed at A4 will not fit cleanly on a US Letter printer, and a US one-pager designed at Letter will print with awkward margins on a UK A4 printer. Letter is wider but shorter than A4 by about 6 mm in each dimension.

The two formats are the dominant 'standard sheet' sizes in their respective regions. A4 is used everywhere except the US, Canada, the Philippines, Mexico and a few Central American countries. Letter is the standard in the US and Canada (and a non-standard secondary option in Mexico). If you are sending a CV or business document across the Atlantic, formatting it for the recipient's region rather than your own is a small touch that saves them from awkward print results.

A4 artwork on a Letter printer typically scales down to 94% of its design size (the 'Fit to Printable Area' default), which adds small white margins on the long edges and shrinks all text proportionally. Designed at 11 pt, you end up reading 10.3 pt on paper, which is fine for body text but makes 8 pt footnote text uncomfortably small. The same effect happens in reverse for Letter on A4.

If the document was designed with bleed (artwork extending past the trim edge for borderless printing), the size mismatch crops the bleed unevenly. A border designed to extend 3 mm past the page edge becomes either a thin visible white strip or a thicker-than-intended border, depending on which way the size mismatch goes. For any document where layout precision matters (CVs, brochures, certificates), set up the document at the recipient's native size rather than yours.

In Microsoft Word, change the page size from File > Page Setup > Paper Size. The default in UK installations is A4; in US installations it is Letter. Switching just the page size scales nothing; it changes the boundary and lets your content reflow. Word also has a 'Scale Content to Paper Size' option in print settings that applies a one-time scale to fit, which is fine for a quick send but ugly for archival use.

In Adobe InDesign, Affinity Publisher and similar layout software, page size is set per document and is fixed at creation. Switching size mid-design requires the 'Layout Adjustment' feature, which scales objects proportionally to the new page size. This works better than Word's approach but still requires manual checks afterwards. The cleanest approach is to design twice (once at A4, once at Letter) for any document destined for both audiences.

Letter size was the de facto US standard by the 1920s, used by typewriter manufacturers and government agencies long before ISO 216 was formalised in 1975. Switching to A4 would have invalidated millions of filing cabinets, pre-printed forms and office supplies. The benefits (mathematical elegance, international consistency) were not enough to offset the costs of replacement. The same inertia kept the US on imperial measurements while the rest of the world standardised on metric.

The result is that the US still operates on a non-ISO 216 paper system, which creates a small but constant friction in international business. Over decades, that friction has been mitigated by smart-scaling print drivers, scaling preferences in word processors and PDF viewers (Acrobat 'Fit to Page' is enabled by default for cross-region printing). For most one-page documents, the difference is invisible to the reader. The [paper size converter](/paper-size-converter) gives the full lookup table across A-series, US Letter, Legal and Tabloid.