Check the resolution of images in a PDF
A photo can look perfect on screen and still print as a blurry, blocky mess. What matters for print is effective resolution: how many image pixels end up in each inch of paper once the picture is placed and scaled on the page. The PDF Resolution Checker measures exactly that for every image in your PDF.
It reports the pixel size, the printed size in inches and millimetres, and the effective PPI of each placement, then flags anything below your print-ready target (300 PPI by default) or below the minimum you accept (150 PPI). Page previews outline every image in green, amber or red so you can see at a glance which picture on which page is the problem.
It is a quick preflight check for brochures, posters, photo books, theses and anything else heading to a printer. The PDF is processed in your browser and never uploaded.
How to use the PDF Resolution Checker
- Set your print-ready target and minimum acceptable resolution, or keep the defaults of 300 and 150 PPI.
- Drop the PDF onto the upload area or click to choose it.
- Read the summary: the number of placements, the lowest PPI and how many fall below each threshold.
- Look at the page previews — red outlines are below the minimum, amber below the target, green print-ready.
- Filter the table to the problem images and download the CSV to share with your designer or print shop.
PDF Resolution Checker features
True effective PPI
Follows every save, restore and transformation in the page’s drawing instructions — including scaled, rotated and nested graphics — to measure how large each image really prints.
Each placement counted
The same image used twice at different sizes is reported twice, because a logo can be sharp at one size and pixelated at another.
Visual page previews
Thumbnails of each page with images outlined and numbered in traffic-light colours.
Your own thresholds
Change the print-ready target and the minimum, and the results update instantly.
Horizontal and vertical PPI
Images stretched unevenly show both values; the lower one decides the status.
Private and offline-friendly
Rendering and analysis use pdf.js in your browser; nothing is sent anywhere.
How effective PPI is calculated
Effective PPI = image width in pixels ÷ printed width in inches (and the same for height). A 1,200 × 800 pixel photo printed 4 inches wide has 1,200 ÷ 4 = 300 PPI. Enlarge the same photo to 8 inches and it drops to 150 PPI; at 16 inches it is only 75 PPI and individual pixels start to show.
The printed size comes from the PDF itself. Every image is drawn into a unit square that the page’s current transformation matrix stretches, rotates and positions, so the checker multiplies those matrices together exactly as a PDF renderer does, including inside form XObjects and annotation appearances.
What resolution do you need?
| Use | Recommended effective PPI |
|---|---|
| Offset and digital press (brochures, books, magazines) | 300 PPI |
| Photo prints and photo books | 240–300 PPI |
| Office laser and inkjet printers | 150–200 PPI |
| Large posters and banners viewed from a distance | 100–150 PPI |
| Screen-only PDFs and presentations | 72–150 PPI |
PPI and DPI — and what to do about low-res images
PPI (pixels per inch) describes images; DPI (dots per inch) strictly describes printer output, but the terms are used interchangeably in print specifications. This tool reports PPI. Note that black-and-white line art such as scanned text or technical drawings is usually expected at 600 PPI or more.
Upscaling a small image in software does not add detail. The real fix is a higher-resolution original, or placing the image smaller. If a file is going online rather than to print, high resolutions just add weight — the PDF Compression Analyzer shows what downsampling would save, and the PDF Image Extractor lets you check the original images themselves.
PDF Resolution Checker FAQ
How do I check the DPI of images in a PDF?
Drop the PDF into the PDF Resolution Checker. Each image placement is listed with its effective PPI (often called DPI), and images below 150 or 300 PPI are flagged in red or amber on page previews.
What is a good resolution for printing a PDF?
For professional print, images should be around 300 PPI at the size they are printed. Office printers are forgiving down to about 150 PPI, and large posters seen from a distance can go lower.
Why does the same image appear twice with different PPI?
It is placed twice at different sizes. Resolution depends on the printed size, so each placement is checked separately.
Does it check vector graphics and text?
No — vectors and text have no fixed resolution and print sharply at any size. Only raster images are measured.
Why are tiny images not listed?
Images of four pixels or fewer are almost always flat colour fills used for backgrounds or shading, so they are ignored to keep the report focused.
Is my PDF uploaded?
No. The file is opened and analysed entirely in your browser.