One page.
Five boundaries.
A PDF has more than one answer to “How big is this page?” The useful answer depends on the boundary you measure.
The five named boxes
| Boundary | What it describes | If absent |
|---|---|---|
| MediaBox | The full physical page extent | Required; may be inherited |
| CropBox | The region used for display or printing | MediaBox |
| TrimBox | The intended finished page after trimming | CropBox |
| BleedBox | The production clipping region around the trim | CropBox |
| ArtBox | The extent of meaningful page content | CropBox |
These definitions and defaults follow the pdf-lib page API and ISO 32000-1, page objects and page boundaries. They describe rectangles, not a certification of the artwork inside them.
A page you can inspect yourself
Download boundary-cases.pdf, open it in the checker, and inspect page 1. All five boxes are explicitly set. They share a center but have different extents:
| Page 1 boundary | Standard points | Inches | Millimeters |
|---|---|---|---|
| MediaBox | 612 × 792 | 8.5 × 11 | 215.9 × 279.4 |
| CropBox / visible | 576 × 756 | 8 × 10.5 | 203.2 × 266.7 |
| TrimBox | 540 × 720 | 7.5 × 10 | 190.5 × 254 |
| BleedBox | 558 × 738 | 7.75 × 10.25 | 196.85 × 260.35 |
| ArtBox | 504 × 684 | 7 × 9.5 | 177.8 × 241.3 |
This sample’s BleedBox extends 9 points beyond each TrimBox edge, equivalent to 0.125 inch or 3.175 mm. That is geometry we intentionally placed in a test document, not a universal bleed recommendation.
When CropBox extends past MediaBox
Page 2 has a CropBox from (-36, 36) to (684, 756), and a MediaBox from (0, 0) to (612, 792). The declared CropBox is 720 × 720 points. Their overlapping visible area is only 612 × 720 points: 215.9 × 254 mm.
PageCaliper shows both quantities: choose CropBox for the declared extent or Visible area for the intersection. This distinction follows the Acrobat coordinate-system documentation. The boundary diagram is unrotated; numerical dimensions include page rotation.
Defaults are not declarations
Many ordinary office PDFs do not explicitly declare TrimBox, BleedBox, or ArtBox. A reader can still return dimensions by following the documented defaults. Our report labels those values “Defaults to CropBox.” This prevents a fallback rectangle from looking like proof of a deliberately configured print boundary.
A BleedBox cannot prove bleed artwork exists. A geometry checker cannot tell whether a photograph actually reaches that rectangle. Inspect the artwork and follow the requirements of the printer receiving the file.
Cropping does not necessarily remove content
Changing a visible boundary can hide content without deleting it. It is not a reliable way to redact a document. Adobe explains this behavior in its PDF cropping documentation. This tool reads boundaries and does not crop or modify files.
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