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PDF to images

How to calculate image size from PDF page size and DPI

By DeckleUpdated

To work out the pixel size of a PDF page exported as an image, multiply the page width and height in inches by the DPI. An A4 page at 150 DPI is about 1240 × 1754 pixels; at 300 DPI it is about 2480 × 3508. In PDF to PNG and PDF to JPG, Screen is 72 DPI, Standard is 150 DPI and Print is 300 DPI.

PDF to PNG

Same physical page, more pixels

150 DPI

Letter: 1,275 × 1,650 pixels

300 DPI

Letter: 2,550 × 3,300 pixels

Double each dimension → four times the pixels

Example calculation · nominal sizes for an 8.5 × 11-inch page. Actual exports depend on page geometry and rounding.

How to calculate image size from DPI

  1. Find the page size. Most documents are A4 (8.27 × 11.69 inches) or US Letter (8.5 × 11 inches).
  2. Pick the DPI you plan to use: 72, 150 or 300.
  3. Multiply the width in inches by the DPI to get the width in pixels.
  4. Multiply the height in inches by the DPI to get the height in pixels.
  5. Multiply the two results to get the total pixels, and divide by one million for megapixels.
  6. Compare the result with what you need: a screen width, a print size or an upload limit.

Example: a Letter page at 150 DPI is 8.5 × 150 = 1275 pixels wide and 11 × 150 = 1650 pixels high. That is about 2.1 megapixels.

Pixel sizes for common pages

PDF pages are measured in points, 72 to the inch, so 72 DPI gives one pixel per point.

Page Screen (72 DPI) Standard (150 DPI) Print (300 DPI)
A4 595 × 842 1240 × 1754 2480 × 3508
US Letter 612 × 792 1275 × 1650 2550 × 3300
A5 420 × 595 874 × 1240 1748 × 2480
A3 842 × 1191 1754 × 2480 3508 × 4961
16:9 slide (13.33 × 7.5 in) 960 × 540 2000 × 1125 4000 × 2250

Landscape pages swap the two numbers. Sizes are rounded up to whole pixels, so a saved image can be one pixel wider than the calculation.

From pixels back to print size

Print size is the pixel size divided by the printing resolution. A 2480-pixel-wide image printed at 300 pixels per inch is 8.27 inches wide, which is A4. The same image printed at 150 pixels per inch is twice as wide but softer.

For a sharp print at the original size, export at Print. For a photo-lab print or a poster, the lab's own guidance on pixels per inch is the figure to aim for.

Why DPI matters for file size and limits

Doubling the DPI doubles the width and the height, so it gives four times as many pixels. Going from Standard to Print turns an A4 page from about 2.2 megapixels into about 8.7, and the file grows roughly in step for PNG.

Each exported image is limited to 16 megapixels on most computers and Android devices, and 4 megapixels on an iPhone, an iPad or a device with little memory. The note under the options in PDF to JPG and PDF to PNG shows the limit for the device you are using. From the table:

  • A4 and Letter at Print are about 8.4–8.7 megapixels: fine on a computer, too large on an iPhone or iPad.
  • A3 at Print is about 17.4 megapixels: above the computer limit too, so use Standard.
  • Every page in the table fits at Standard on any device except A3, which is 4.4 megapixels and too large on an iPhone or iPad at that setting.

Deckle checks every selected page before it writes the first image. If one is over the limit, nothing is exported. Lower the resolution and export again, or export the large page on its own.

Tips

  • Size for the place the image is shown. A web column 800 pixels wide gains nothing from a 2480-pixel image except download time.
  • Use Print when you will crop. Cutting a chart out of a page leaves fewer pixels; start with more.
  • Mind mixed page sizes. A PDF with an A3 fold-out among A4 pages gives one larger image; check its size separately.
  • DPI does not sharpen a scan. A page scanned at 150 DPI exported at Print gets bigger, not clearer. See why an export looks blurry.

Frequently asked questions

What DPI should I use for printing?

Print (300 DPI). It gives enough pixels for a sharp print at the page's original size.

What DPI is best for a website?

Standard (150 DPI) for full pages people will read, and Screen (72 DPI) for thumbnails.

Can I export at 600 DPI?

No. Deckle offers up to 300 DPI. At 600 DPI an A4 page would be about 35 megapixels, over the per-image limit on every device.

Does DPI change the image or just a label in the file?

It changes the image. Higher DPI renders the page with more pixels, so detail is real, not stretched.

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