A4 vs Letter

A4 is taller by 17.6 mm and narrower by 5.9 mm. By area A4 is 62,370 mm² and Letter is 60,323 mm², so A4 is about 3 percent larger.

Choose fit to page, or set the scale to 94 percent. The content will shrink slightly and leave wider side margins. Do not print at 100 percent or the bottom 18 mm will be cut off.

The file is set to Letter and the tray holds A4, or the reverse. A4 is 18 mm taller, so a Letter page leaves a blank strip at the bottom of an A4 sheet. Match the page size to the paper.

Keep everything inside a 200 × 270 mm (7.9 × 10.6 in) safe area centred on the page. It fits within both sheets, so the document prints at 100% on either without cropping. On A4 that means margins of at least 5 mm left and right and 13.5 mm top and bottom; on Letter, 8 mm and 4.7 mm. Keep headers and page numbers inside the area too, and send a PDF so the recipient's software cannot reflow the text.

In Word, choose Layout, Size and the sheet; to make it stick, open the Page Setup dialog, pick the size and click Set As Default. Word also has a setting under Options, Advanced, Print, "Scale content for A4 or 8.5 × 11 paper sizes", which resizes documents at print time and is on by default. In Google Docs, choose File, Page setup, Paper size, then Set as default.

Usually not. With the same 25 mm margins the text area changes from 160 × 247 mm on A4 to 166 × 229 mm on Letter, so each page holds fewer lines and a 40-page A4 report typically runs to 42 or 43 Letter pages. Check page references and the table of contents after switching.

Because they sit below the end of the Letter sheet. A footer 10 mm from the bottom of an A4 page is 287 mm from the top, past Letter's 279.4 mm length, so at 100% it is cut off. Print with Fit to page (94%) or keep footers inside the shared 200 × 270 mm area.

A No. 10 (4 1/8 × 9 1/2 in, 104.8 × 241.3 mm) takes Letter folded in thirds, and a DL (110 × 220 mm) takes A4 folded in thirds. They also cross over: A4 folded in thirds fits a No. 10 with room to spare, and Letter folded in thirds fits a DL with about 2 mm each side. Flat, Letter fits a C4 and A4 fits a 9 × 12 in catalog envelope.