PDF Page Dimensions

Every page in a PDF document carries a set of rectangular boundaries called page boxes. These boxes, defined in the PDF specification (ISO 32000), control how the page is displayed, printed, and trimmed. Understanding them is essential for anyone working in prepress, print production, or document quality control.

The five PDF page boxes

The MediaBox is the only required box. It defines the full extent of the physical medium — the maximum boundary of the page. All other boxes must fall within or be equal to the MediaBox. When no other boxes are defined, viewers and printers treat the MediaBox as the effective page boundary for all purposes.

The CropBox defines the region to which the page contents are clipped when displayed or printed. In most PDF viewers, this is the visible area. If a CropBox is smaller than the MediaBox, content outside the CropBox exists in the file but is hidden from view. CropBox defaults to MediaBox when not explicitly set.

The BleedBox defines the region to which the page contents should be clipped in a production environment. It typically extends 3-5 mm beyond the TrimBox on all sides. This bleed area accounts for imprecision in the cutting process — when a stack of pages is trimmed, slight shifts are inevitable, and bleed ensures that color or imagery extends all the way to the trimmed edge rather than leaving a white strip.

The TrimBox defines the intended finished size of the page after trimming. In print production, the TrimBox is the final cut line. A standard A4 document with 3 mm bleed would have a TrimBox of 210 x 297 mm and a BleedBox of 216 x 303 mm. The TrimBox is the most important box for commercial printers because it defines the exact dimensions of the finished product.

The ArtBox defines the extent of the meaningful content on the page. In publishing workflows, the ArtBox marks where the actual design or text content lives, excluding margins, running headers, and page numbers. It is the least commonly used box and is entirely optional.

The /Rotate flag and its impact

PDF pages have a /Rotate entry that specifies a clockwise rotation angle (0, 90, 180, or 270 degrees) applied when rendering the page. This rotation affects only the visual presentation — the underlying page box coordinates remain unchanged. A page whose MediaBox is 595 x 842 points (portrait A4) with /Rotate set to 90 will appear as a landscape page measuring 842 x 595 points. This distinction matters when preparing documents for print, because the physical page box defines the paper size to use, while /Rotate controls how content is oriented on that paper.

PDF coordinate system and units

All PDF page box dimensions are specified in PDF points. One point equals exactly 1/72 of an inch (0.352778 mm). This unit system dates back to PostScript and provides sufficient precision for print production while keeping coordinate values as convenient numbers. An A4 page measures 595.28 x 841.89 points, US Letter is 612 x 792 points, and US Legal is 612 x 1008 points. The origin (0, 0) of the coordinate system is at the bottom-left corner of the MediaBox by convention, with x increasing to the right and y increasing upward.

This tool uses pdf-lib, a JavaScript library for PDF parsing that runs entirely in your browser. It reads each page's dictionary entries to extract box definitions, rotation values, and structural metadata without modifying the document in any way. The analysis is read-only — your PDF is never altered.

Knowing your PDF's page dimensions and box definitions is critical in many professional contexts:

• Print prepress validation — Commercial printers require specific TrimBox and BleedBox settings. Submitting a file without a defined TrimBox or with insufficient bleed causes production delays and reprints. Checking dimensions before submission catches these issues early.
• Mixed-size document auditing — Merged PDFs frequently contain pages of different sizes. A legal filing scanned from mixed-format originals might have Letter, A4, and Legal pages interleaved. Identifying the size of each page helps determine whether resizing or reprocessing is needed.
• Poster and large-format printing — Large-format printers need exact dimensions to calculate media usage and cost. A poster file must match the ordered print size precisely — verifying the MediaBox confirms whether the artwork was created at the correct scale.
• Ebook and digital publishing — Digital publishing platforms have page dimension requirements. Verifying that a PDF meets the target dimensions (for example, 6 x 9 inches for a standard trade paperback) prevents rejection during the upload review process.
• Architectural and engineering drawings — CAD exports to PDF may use non-standard page sizes (ANSI D, ARCH E, custom sheet sizes). Confirming the actual dimensions ensures the drawing prints at the correct scale factor and that 1:1 measurements on the printed sheet match the intended dimensions.
• Rotation troubleshooting — When a PDF page appears rotated but content editing tools show it as portrait, the /Rotate flag is the cause. Understanding whether a page is structurally rotated (via /Rotate) or was created in landscape orientation (wider MediaBox) determines the correct fix.

Analyzing PDF dimensions locally in your browser eliminates the need to upload files to cloud services. Documents containing architectural plans, legal filings, unpublished manuscripts, or proprietary designs remain entirely on your device. No file data is transmitted, stored, or logged by any server.