A4, US Letter or 16:9: which PDF page size should you use?

Updated: 2026-10-14 · Dawwerni team

Use 16:9 (13.333 x 7.5 in, the PowerPoint widescreen size) for slides shown on screens, A4 (210 x 297 mm) for documents read or printed outside North America, and US Letter (8.5 x 11 in) for documents for the US and Canada. In CSS, 1 inch equals 96 px, so A4 is about 794 x 1123 px.

The three sizes you actually need

Paper formats run into the dozens, but when you turn an HTML page into a PDF, three sizes cover almost every case: the international A4 sheet, the North American Letter sheet and the 16:9 widescreen slide. Picking the right one first saves you from the most common export problems: slides with white bands, documents with a cut-off right column, or a report that prints badly at the client's office.

Every major tool supports all three, including our free HTML to PDF converter, which offers A4, US Letter and 16:9 slides in portrait or landscape with adjustable margins.

How CSS pixels map to millimetres and inches

CSS defines its units on a fixed ratio: 1in = 96px, 1in = 2.54cm, so 1cm is about 37.8px and 1mm is about 3.78px. These are CSS pixels, not physical screen pixels, which is why the numbers stay the same on a phone, a laptop or a 4K monitor. When a browser prints, it lays the page out on a sheet using exactly this ratio.

This gives you a simple way to design pages that fit: take the paper width, subtract the margins, and convert to px. Your content should not be wider than that number, or the browser will shrink it or cut it off.

/* a document column that fits A4 with 12 mm margins */
main {
  max-width: 186mm;   /* the browser converts mm for you */
  margin: 0 auto;
}

When to use 16:9 for slides

If the PDF will be projected, shared on screen or opened next to a PowerPoint file, use 16:9. It is the default slide size in PowerPoint (Widescreen, 13.333 x 7.5 in), in Google Slides and in Keynote themes, and it matches the shape of almost every laptop, TV and projector. A 16:9 slide printed on A4 landscape leaves bands at the top and bottom; an A4 page shown full-screen leaves bands on the sides.

HTML decks are usually designed on a fixed stage of 1920 x 1080 or 1280 x 720 pixels. Both are 16:9, so they scale onto a 13.333 x 7.5 in page without distortion: 1280 px is exactly 13.333 in at 96 px per inch, and a 1920 px stage is simply scaled by two thirds. Our converter detects such 16:9 sections, .slide elements and reveal.js decks and turns each one into its own page. The detailed rules for building those slides are in HTML slides to PPTX without losing the design.

/* a 16:9 PDF page with one slide per page */
@page {
  size: 13.333in 7.5in;
  margin: 0;
}
.slide {
  width: 13.333in;
  height: 7.5in;
  overflow: hidden;
  break-after: page;
}

A4 or US Letter for documents

The rule is about your reader, not about you. A4 is the standard in Europe, Africa, the Middle East, most of Asia and Oceania. US Letter is the standard in the United States and Canada and is common in Mexico and the Philippines. If a document will be printed, it should match the paper in the reader's printer: an A4 file printed on Letter loses a little at the bottom or gets scaled down; a Letter file printed on A4 gets a slightly wider page with an empty strip at the bottom.

When you do not know where the reader is, A4 with generous margins (at least 15 to 20 mm) is a sensible default: A4 is narrower but taller than Letter, and print dialogs usually offer a fit-to-page option, so wide margins keep the content clear of the edges when the sheet is scaled. For screen-only reading, either format is fine.

• Invoices, contracts, CVs: match the reader's country.
• Internal reports in an international team: A4 unless the company standard says otherwise.
• Forms people print and fill by hand: always match the local paper.
• Dashboards and wide tables: consider A4 or Letter in landscape rather than shrinking text.

Setting the size with @page

The CSS @page rule tells the print engine which sheet to use. It accepts keywords (A4, A5, A3, letter, legal), an orientation (portrait, landscape), or explicit width and height. Chromium-based browsers (Chrome, Edge, Brave, Opera) and recent versions of Firefox honour it, and in Chrome a page that sets a size usually locks the paper size option in the print dialog. Safari has historically given less control, so on a Mac it is worth checking the paper size in the print dialog as well.

/* A4 portrait with 12 mm margins */
@page { size: A4; margin: 12mm; }

/* US Letter landscape */
@page { size: letter landscape; margin: 0.5in; }

/* the first page without a top margin (cover) */
@page :first { margin-top: 0; }

/* keep backgrounds and dark themes when printing */
html { -webkit-print-color-adjust: exact; print-color-adjust: exact; }

Margins: in CSS or in the print dialog

Margins can come from three places: @page { margin }, the print dialog (Default, None, Minimum or Custom in Chrome) and the page's own padding. If you set them in CSS, choose "Default" in the dialog so the browser uses your values. For slides, use zero page margins and keep the safe area inside the slide design. Note that the print dialog's "Headers and footers" option prints the date, title and URL inside the margins; turn it off for clean output.

Portrait or landscape?

Portrait suits text: lines stay at a comfortable reading length and pages scroll naturally on a phone. Landscape suits wide content: tables with many columns, timelines, dashboards and anything designed for a screen. If your HTML was designed at desktop width (1200 px or more) and you print it on A4 portrait, the browser has only about 700 px to work with, so it either scales everything down to small text or the responsive layout switches to its narrow version. Landscape A4 gives roughly 1030 px of width with 12 mm margins, which is often enough to keep the desktop layout.

Exporting with the right size in practice

1. Decide the reader first: on screen (16:9), printed in the US or Canada (Letter), printed elsewhere (A4).
2. Check your layout width against the printable width table above.
3. Add an @page rule if you control the HTML, or ask the AI that generated it to add one.
4. Open the free HTML to PDF tool, drop the file, pick the page size, orientation and margins.
5. Choose "Print / Save as PDF" for selectable text and small files, or "Download PDF" for a one-click, pixel-faithful copy where text is not selectable.
6. Open the result and scroll through every page before sending it.

The two export modes are compared in 3 free ways to convert HTML to PDF. If pages come out with cut lines or a white background, see why your HTML to PDF looks broken, and for the full set of print rules, the print CSS cheat sheet.