PDF Page Size
Every PDF page has a set of rectangular boxes that define different aspects of its geometry. These boxes are not visual elements — they are coordinate values stored in the page dictionary that tell PDF viewers and printers how to handle the page. Understanding the box hierarchy is essential for print production work, for correcting pages with incorrect margins, and for any PDF workflow that requires precise page geometry control.
The five page boxes are: <strong>MediaBox</strong> (the physical sheet), <strong>CropBox</strong> (the visible area), <strong>TrimBox</strong> (the finished document size after trimming), <strong>BleedBox</strong> (the bleed area for safe print trimming), and <strong>ArtBox</strong> (the meaningful content area). Only MediaBox is required; the others are optional.
The five PDF page boxes
<strong>MediaBox</strong> (required) — The physical sheet size. Defines the complete physical medium on which the page will be printed or displayed. All other boxes must be within or equal to the MediaBox. For most documents, the MediaBox equals the page's visible size. In print production, the MediaBox includes any printer's marks, bleed, and white space around the document. Example: A4 MediaBox = <code>[0 0 595.28 841.89]</code> (in PDF points).
<strong>CropBox</strong> (optional) — The region displayed by viewers and printed by default. If CropBox is absent, the MediaBox is used. PDF viewers clip display to the CropBox. Printers use the CropBox as the default print region. The CropBox is useful for hiding content that exists in the file (crop marks, bleed) from screen display while keeping it available in the PDF. Defaults to MediaBox if not specified.
<strong>TrimBox</strong> (optional) — The intended dimensions of the finished document after trimming. Used in print production to specify the final page size after cutting. For example, a business card PDF may have a MediaBox including bleed, a BleedBox with the 3mm bleed, and a TrimBox at the exact finished size. PDF/X requires TrimBox for all page configurations. Defaults to CropBox if not specified.
<strong>BleedBox</strong> (optional) — The region to which the page content should be clipped when output in a production environment. Extends beyond the TrimBox to provide the bleed margin — typically 3mm on each side. Content that extends to the BleedBox edge is cut off during trimming without leaving white gaps at the trim edge. Defaults to CropBox if not specified.
<strong>ArtBox</strong> (optional) — The extent of meaningful content (artwork) intended to be placed in a larger composition. Used for imported PDF pages to indicate the content region to be used. Rarely used in practice. Defaults to CropBox if not specified.
Standard page sizes in PDF points
PDF dimensions are specified in PDF points: 1 point = 1/72 inch. Standard page sizes:
<strong>ISO 216 A-series (mm → points)</strong>: - A0: 841 × 1189 mm → 2383.94 × 3370.39 pt - A1: 594 × 841 mm → 1683.78 × 2383.94 pt - A2: 420 × 594 mm → 1190.55 × 1683.78 pt - A3: 297 × 420 mm → 841.89 × 1190.55 pt - A4: 210 × 297 mm → 595.28 × 841.89 pt (most common worldwide) - A5: 148 × 210 mm → 419.53 × 595.28 pt - A6: 105 × 148 mm → 297.64 × 419.53 pt
<strong>US/North American sizes (inch → points)</strong>: - US Letter: 8.5 × 11 in → 612 × 792 pt (dominant in North America) - US Legal: 8.5 × 14 in → 612 × 1008 pt - US Tabloid (Ledger): 11 × 17 in → 792 × 1224 pt - US Executive: 7.25 × 10.5 in → 522 × 756 pt
<strong>Conversion formulas</strong>: - mm to points: multiply by 72/25.4 ≈ 2.8346 - inches to points: multiply by 72 - points to mm: multiply by 25.4/72 ≈ 0.3528
<strong>Custom page sizes</strong> — Any dimensions are valid. Posters, labels, envelopes, business cards, and large-format prints all use custom MediaBox values. There is no minimum or maximum size specified by the PDF standard, though very large pages (>200 inches) may cause issues with some RIPs and viewers.
Inspecting and fixing page boxes
<strong>Inspecting boxes</strong>: - Acrobat Pro: Tools > Print Production > Crop Pages shows all five box values - qpdf: <code>qpdf --json input.pdf | python3 -m json.tool | grep -A5 MediaBox</code> - PyMuPDF: <code>page.mediabox</code>, <code>page.cropbox</code>, <code>page.trimbox</code> - Poppler: <code>pdfinfo -box input.pdf</code> shows MediaBox and CropBox
<strong>Common problems and fixes</strong>:
<strong>CropBox smaller than content</strong> — Content outside the CropBox is invisible in viewers but present in the file. A PDF that "cuts off" content may have a CropBox set too small. Fix: expand the CropBox to match the MediaBox.
<strong>Wrong page size in Word export</strong> — Word's "Save as PDF" uses the printer's page size, not the document's page size. If the default printer is Letter but the document was designed for A4, the PDF will have a Letter MediaBox. Fix: set the printer to "Microsoft Print to PDF" or use "Export to PDF" with correct size settings.
<strong>Print production bleed setup</strong> — For print production, the workflow is: 1. MediaBox = TrimBox + 6mm (3mm bleed each side) 2. BleedBox = TrimBox + 6mm (same as MediaBox for 3mm bleed) 3. TrimBox = final finished size 4. CropBox = MediaBox (show full page in viewer)
Frequently asked questions
Why does my PDF look different sizes in different viewers?
Different PDF viewers use different boxes as their default display region. Most viewers (Acrobat, Chrome, Firefox) display the CropBox. If the CropBox is smaller than the MediaBox (a common print production setup where the MediaBox includes bleed and crop marks), viewers clipping to the CropBox will show a smaller area than the full MediaBox. Some specialised viewers or export operations that read the MediaBox will show the larger area including bleed. Additionally, some documents have per-page boxes set differently — pages with different CropBox values will appear different sizes. Check all five box values to diagnose apparent size inconsistencies.
What is the bleed and why does print production require it?
Bleed is extra content that extends beyond the intended trim edge of a printed document. When a printing press cuts pages to the finished size, the cutting mechanism has a tolerance of ±1–2mm. If content is designed to print exactly to the edge (a background colour that fills the page, for example), a small cutting error will leave a thin white strip at the edge. The bleed extends background and edge content by 3mm beyond the trim edge, so even if the cut is 2mm off, the content still reaches the edge. The TrimBox specifies the intended cut line; the BleedBox specifies the bleed extent. Content must extend to the BleedBox for print files; finished documents show only to the TrimBox.
How do I change a PDF's page size without reprinting?
Changing a PDF's page size involves modifying the MediaBox (and potentially CropBox) in the page dictionary. Options: (1) Adobe Acrobat Pro > Tools > Print Production > Crop Pages: set new box values interactively. (2) qpdf command-line: qpdf --job-json-file resize.json input.pdf output.pdf with appropriate resize parameters. (3) PyMuPDF: page.set_mediabox(fitz.Rect(0, 0, width, height)). (4) Ghostscript: gs -dBATCH -dNOPAUSE -sDEVICE=pdfwrite -dDEVICEWIDTHPOINTS=612 -dDEVICEHEIGHTPOINTS=792 output.pdf input.pdf — this re-renders the page, which may shift content. Modifying box values changes the declared geometry; content outside the new box is clipped. Scaling content to fit a new size requires transformation operations.