PDF DPI Checker
Validate effective image resolution before upload. This tool converts pixel dimensions and placed size into DPI so you can identify weak assets early.
DPI Check
Enter source pixels and final placed size in inches.
DPI X
300.0
DPI Y
300.0
Effective DPI
300.0
How It Works
Effective DPI is determined by dividing image pixels by placed dimensions in inches. If an asset is enlarged in layout, effective DPI falls even when the source file is large.
The checker reports axis DPI and effective DPI (minimum of X/Y), then classifies output as PASS, WARN, or FAIL based on print-safe thresholds.
Decision Thresholds
- PASS: effective DPI ≥ 300
- WARN: 240 ≤ effective DPI < 300
- FAIL: effective DPI < 240
Use WARN as a review state. Large backgrounds and grayscale photography are often where quality drops first.
Common Mistakes
- Checking source DPI only, ignoring placed size in final layout.
- Using web-optimized images for print sections.
- Exporting from compressed workflows that downsample assets.
- Treating preview quality as proof of print quality.
What This Tool Does
The PDF DPI Checker estimates effective print resolution by comparing source pixel dimensions with the size the image occupies on the printed page. That matters because print quality is driven by effective DPI, not just the resolution shown in an image editor. A large image file can still print poorly if it is stretched too far inside the layout.
This tool gives a fast preflight answer before you upload. Instead of waiting for a platform to warn that images are low resolution, you can test the assets used in charts, full-page artwork, chapter openers, and cover elements while you still control the source layout. It is most useful when several people have touched the files and image placement rules are no longer obvious.
Why This Matters
KDP and IngramSpark accept PDF files, but both platforms still care about the print integrity of the images inside those PDFs. Low-resolution assets often look fine on a laptop preview because screens hide the loss of detail that becomes obvious in print. When the effective DPI drops too far, photos can look muddy, line art can break apart, and text embedded in graphics becomes soft or unreadable.
Resolution errors also create rework across the whole production chain. If you discover them late, you may need to replace source files, re-export pages, rebuild the PDF, and then recheck trim, bleed, and pagination. That is why resolution checks belong near the start of a preflight workflow rather than at the very end.
Common Errors
- Using website graphics or social-media exports in a print interior.
- Upscaling a small image and assuming the larger dimensions improve actual quality.
- Placing a 300 DPI asset at a much larger physical size inside the layout.
- Letting export compression downsample images below the intended threshold.
- Checking nominal image resolution but ignoring the placed size on the page.
- Assuming a crisp on-screen preview means the PDF is print-ready.
How the Calculation Works
The calculation is straightforward: effective DPI equals the number of pixels divided by the physical size used in print. If an image is 2400 pixels wide and placed at 8 inches, the horizontal effective resolution is 300 DPI. If that same asset is enlarged to 10 inches, the effective resolution drops to 240 DPI without changing the original file. This is why layout decisions matter as much as the source asset itself.
The checker evaluates both axes and reports the limiting value. In real books, the weaker axis controls output quality because an image can only print as sharply as its lowest effective resolution. The pass, warning, and fail bands are meant to surface risk quickly so you can replace, resize, or re-export the image before the issue spreads into later revisions.
When To Use This Tool
Use this checker after placing images and before final PDF export, then again if the layout changes significantly. It is particularly important for books with photography, diagrams, workbooks, or covers that rely on fine detail. Any time you enlarge an image, change trim size, or switch export presets, you should expect the effective DPI risk profile to change.
In a practical workflow, run DPI checks before page-level geometry checks. If image quality is already failing, there is no value in polishing margins or bleed around assets that need to be replaced. Once the images pass, move on to trim, bleed, and margin validation, then finish with upload checklist and platform preview.
Diagnostic Workflow
Review the images most likely to fail first: full-page artwork, detailed charts, screenshots, and any image that was enlarged during layout. Compare their pixel dimensions to the actual placed size in the book, then use this checker to identify the weakest assets. If one critical image fails, replace or resize it before final export rather than hoping compression settings will rescue the result.
After replacing assets, rerun the check and only then move to PDF-level preflight. That order keeps image quality issues from being confused with margin, trim, or bleed problems later in the workflow.
It is also worth checking image classes separately. Decorative textures may tolerate lower effective DPI than instructional diagrams, screenshots, or small text embedded inside graphics. Reviewing assets by function instead of by file size gives you a better sense of which failures are cosmetic and which ones are likely to degrade the printed book in obvious ways.