PDF DPI Checker

1. Select and measure

   Drop one PDF, up to 50 MB, or load a sample. Every page is inspected locally with no daily inspection cap.

2. Locate the risk

   Confirm trim dimensions, choose your target and click an issue or image row. The viewer changes page and frames its measured bounds.

3. Compare the proposal

   Change bleed amount, edge method or marks. Inspect four corners; original DPI, font, color and safety warnings remain available.

4. Choose the right file

   Download a limited proof or TXT sample. Production PDFs and full reports require Pro access and confirmed print specifications.

The practical print question is how many image pixels occupy one physical inch on the page. A pixel count or a JPEG resolution tag cannot answer that alone. This checker reads the image width and height and follows the cumulative PDF graphics transform to measure its placed dimensions. Every occurrence gets its own table row.

The brochure’s image has 710 × 426 pixels and is drawn at 360 × 216 points. Since 72 points equal one inch, the placed size is 5 × 3 in. Dividing pixels by inches yields 142 × 142 DPI. Nothing in that result depends on the PDF file’s compressed byte size or its filename.

The technical sample makes the transform visible through numbers. A 600 × 300 pixel image at 144 × 72 points gives 300 × 300 DPI. Rotate that placement by 90 degrees and the physical basis lengths remain unchanged. Stretch its horizontal basis to 288 points and the result becomes 150 × 300 DPI.

An axis-aligned bounding rectangle is useful for highlighting, but not for computing rotated-image DPI. The inspector uses the lengths of the two transformed basis vectors. It composes graphics-state matrices through q/Q saves, cm operations and nested Form XObjects, and applies the page UserUnit before converting points to inches.

The same image resource can be reused on another page or within a Form at another scale. Counting unique resources would miss this difference. In the CTM example there are five placements across two pages, including a nested Form and a second-page use at 150 × 300 DPI. Click that placement to inspect its actual bounds.

Changing the minimum from 300 to 150 DPI changes the classification, never the measured resolution. At the lower target, a 150 × 300 placement meets both axes. Whether that target suits a poster, a book image or a close-viewed card is a job decision. The tool does not invent a different physical measurement to produce a PASS.

The 300 DPI size table rounds pixel counts to the nearest whole pixel. An A4 page is 210 × 297 mm, producing approximately 2480 × 3508 pixels. Bleed adds physical area outside trim and therefore needs additional pixels when producing a full-page raster. The printed trim size must remain separate from that outer canvas.

Rasterizing a page at 600 DPI does not make a low-detail image sharper. It samples the existing page more densely and can preserve vector edges at the chosen output scale. Photographic detail remains limited by the original placement. Request a better source image, reduce the placed dimensions or record the printer’s explicit resolution exception.

300 DPI: physical size to pixels

Pixels = millimeters ÷ 25.4 × 300, rounded to the nearest whole pixel. These dimensions refer to the trim, before adding any bleed. A different placement size changes effective DPI even when the underlying pixels are unchanged.

Bleed and safety: keep the directions separate

Bleed extends outward; the safe margin sits inward. The numerical targets below are inspection examples. A book cover, folded piece, bound page or large-format print must use its actual job template. KDP spine and safety requirements cannot be inferred from the example’s fixed dimensions.

Before the final handoff

For business cards and mailers, review the smallest type and border lines as well as the background edge. For folded brochures, include fold tolerances in the source layout. For a full book cover, verify the entire wrap and spine against the supplied template. These tasks share PDF geometry but have different finishing risks.

Use the print-ready PDF checklist and bleed guide for the cut, bleed and safe-area sequence. Use the color, font and hairline guide to interpret mixed objects, embedded programs and black-overprint requirements before authorizing a production repair.