Your printer rejected the file, or worse, printed it and the result looks soft. Somewhere in the email is the phrase "please supply at 300 DPI", and you are staring at a PDF wondering where that number is even kept.
Short answer: it is not kept anywhere. A PDF has no DPI of its own. It has a page size, and it has content placed on that page — and any raster image among that content has a resolution that only means something once you know how large it has been placed.
That distinction is the whole subject.
Effective resolution, in one line of arithmetic
effective DPI = image pixel width ÷ placed width in inchesA 3000 px wide image placed 10 inches wide is 300 DPI. The same image stretched to 20 inches is 150 DPI. Nothing about the file changed — only the size it is being asked to fill.
This is why "what DPI is this PDF" is not quite answerable, and why the number reported in one tool disagrees with another. One is reporting the image's own resolution, the other is reporting what it comes to after scaling.
The effective figure is the one the printer means.
Checking it in Acrobat Pro
The most direct route, if you have it:
- Tools > Print Production > Output Preview
- Tick Object Inspector at the bottom of the panel
- Click any image on the page
The panel lists that object's colour space and its resolution as placed. Click each image in turn — a file is only as good as its weakest one.
For a whole-document verdict rather than a click-by-click one, Print Production > Preflight has profiles that flag every image under a threshold you set. Run "Digital printing (colour)" or build a custom profile with your printer's minimum, and it returns a list rather than making you hunt.
Checking it without Acrobat Pro
Acrobat Reader will not tell you. These will:
Illustrator or InDesign. Place or open the PDF, open the Links panel, select the image, expand the panel's info. Both the actual PPI and the effective PPI are listed, side by side, which makes the scaling issue obvious.
Preview, on a Mac. Tools > Show Inspector reports page size but not per-image resolution. Useful for confirming the physical dimensions, which is half the calculation — you can then do the division yourself if you know the source image's pixel size.
Ghostscript, if you are comfortable at a command line, will list image dimensions per page. Precise, and considerably more effort than the problem usually deserves.
An online checker. Our print file checker reads a PDF, JPEG or PNG, reports the effective resolution at the size you intend to print, and says plainly whether it clears the threshold for that size. Free, no account, no upload of anything you would not email a printer anyway.
What number do you actually need?
The 300 DPI convention comes from offset printing of material held in the hand. It is a sensible default and a poor universal rule.
| Product | Sensible minimum | Why |
|---|---|---|
| Greetings cards, business cards | 300 DPI | Held at 30 cm; detail is scrutinised |
| A4 and A3 art prints | 300 DPI | Same, and buyers inspect fine linework |
| Posters, 50 × 70 cm and up | 200–300 DPI | Viewed at a metre or more |
| Large canvas, 90 cm and up | 150 DPI | Viewed across a room; canvas texture hides more than paper does |
| T-shirts (DTG) | 150–300 DPI | Fabric weave limits detail regardless |
| Mugs, sublimation | 300 DPI | Small area, close inspection |
The pattern is viewing distance, not product prestige. A billboard runs at 20 DPI and looks perfect from the road.
Our print resolution and DPI guide works through the maths for each size, and the poster print file size reference has the pixel dimensions for standard print sizes so you can check a file against its intended size in one step.
When it comes up short
In order of how much they help:
- Print smaller. A file that fails at 70 × 100 cm may pass comfortably at 50 × 70. Changing the size you offer is instant and costs nothing.
- Rebuild from the source. If the artwork began as a vector, a Procreate canvas or an AI generation you can re-run at a higher resolution, regenerate the export at the size you need. This is the only fix that adds real detail.
- Resample, carefully, as a last resort. Photoshop's Preserve Details 2.0 and the various AI upscalers do a respectable job on photographic content and a poor one on hard edges and text. They interpolate — they estimate what would plausibly sit between the pixels you have. Nothing recovers detail that was never recorded.
- Reconsider the medium. Canvas, textured art paper and fabric are all forgiving of lower resolution in a way that gloss photo paper is not.
What does not work: re-saving at a higher DPI setting without resampling. That changes the metadata and the implied print size, and leaves the pixels exactly as they were.
The trap specific to print-on-demand
A mockup is not a print file, and the two get confused constantly.
Your listing images can be 2000 px square and look immaculate on Etsy — that is a screen at roughly 72 to 150 DPI, and it proves nothing about whether the underlying artwork will survive being printed at 60 cm. Sellers discover this when the first physical order arrives.
Keep them separate:
- Master artwork: the largest size you intend to sell, at the resolution that size demands. Everything else derives from it.
- Print file: exported from the master to the printer's exact template and bleed.
- Listing images: rendered mockups, sized for Etsy's image requirements.
Get the master right and the other two are exports. Get it wrong and no amount of mockup polish hides it.
What should I do?
- Find the effective resolution of every image in the PDF — Object Inspector in Acrobat, the Links panel in Illustrator, or a print file checker.
- Compare it against the size you actually sell, not against a blanket 300.
- If it fails, shrink the offered size first — it is the only fix that is free and certain.
- Regenerate from the source where one exists, rather than upscaling the export.
- Check the master, not the mockup, before a design goes on sale. A soft print is a refund and a review; both are more expensive than five minutes of checking.
A PDF has no DPI. It has images, sizes, and a division you can do in your head — and the answer to that division is what your printer is asking for.
Frequently asked questions
How do I check the DPI of a PDF?
Open it in Acrobat Pro and use Print Production > Preflight, or Tools > Print Production > Output Preview with Object Inspector, then click the image — the panel reports its effective resolution at the size it is placed. Free alternatives: place the PDF in Illustrator or InDesign and read the Links panel, or run it through an online print file checker.
Why does my PDF show two different DPI numbers?
One is the image's native resolution, the other is its effective resolution after scaling. Shrink a 300 DPI image to half size on the page and its effective resolution doubles to 600; enlarge it and it drops. Effective resolution is the only one the printer cares about.
Is 150 DPI good enough for printing?
It depends entirely on viewing distance. For a business card or a greetings card held at arm's length, no. For a large canvas or a poster viewed from two metres away, 150 DPI is genuinely fine and is what many large-format printers work to. The closer the print is held, the higher the requirement.
Can I increase the DPI of a PDF?
You can change the number; you cannot add detail that was never captured. Resampling invents pixels by interpolation, which softens edges rather than sharpening them. The only real fix is to rebuild the file from the original artwork at the correct size, or to print smaller.
Does vector artwork in a PDF have a DPI?
No. Vector paths and live text are resolution-independent and print at whatever resolution the RIP renders them, which is usually far higher than any raster image alongside them. Only the placed images in a PDF have a resolution that can be too low.