Resize a PDF on Mac: Page Size or File Size?
“Resize a PDF” means two different jobs. To change the page size (A4, Letter), print to PDF with a new paper size and Scale to Fit. To change the file size (megabytes), use Preview’s Reduce File Size filter or a PDF compressor. In our test, changing page size did not shrink the file.
Do I need to change the page size or the file size?
Page size is the physical dimensions of each page, such as A4 or US Letter. File size is how many bytes the PDF takes up. They are independent. A photo PDF can be a huge file on a small page, and a text PDF can be a tiny file on a poster-sized page.
We built a single-page PDF from a photo: 768 by 768 points and 319,020 bytes. We then changed the page to A5 (420 by 595 points) and, separately, compressed it at the same page size.
| Operation | Page size after | File size after |
|---|---|---|
| Original | 768 x 768 pt | 319,020 bytes |
| Fit to A5 page | 420 x 595 pt | 319,166 bytes |
| Compress (screen-resolution images) | 768 x 768 pt | 116,263 bytes |
Shrinking the page left the file the same size, because the embedded photo was not touched. Compression cut the file by roughly two thirds and left the page alone. One photo and one run, so read these as an illustration, not a promise. Real results depend on what is inside the PDF.
How do I change the page size of a PDF on a Mac?
macOS has no “resize pages” button, but the print dialog does the job:
- Open the PDF in Preview and choose File > Print.
- Set Paper Size to the target, such as A4 or US Letter.
- Under Preview in the options list, turn on Scale to Fit.
- Click the PDF menu at the bottom left and choose Save as PDF.
Check the result in Preview with Tools > Show Inspector. This re-lays out each page onto the new paper, so margins may shift if the aspect ratios differ. For a command-line route, Ghostscript (install it with Homebrew) can fit every page to a paper size:
gs -o a4.pdf -sDEVICE=pdfwrite -sPAPERSIZE=a4 -dFIXEDMEDIA -dPDFFitPage input.pdfThat is the command we used for the A5 run above. Pages are scaled to fit, not cropped.
How do I reduce the file size of a PDF on a Mac?
In Preview, choose File > Export, open the Quartz Filter menu and pick Reduce File Size. It is free and quick, but it applies one fixed level and often makes images soft, which our Preview guide measures. For control, see how to compress a PDF on Mac and the best PDF compressor for Mac roundup.
Our Ghostscript run used the screen-resolution setting that lowers image quality. It is the same idea in the shell:
gs -q -o small.pdf -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook input.pdfPick /screen for the smallest file, /ebook for a middle ground, and /printer when quality matters. Look at the result at full zoom before sending it.
Why will my PDF still not upload after I resized it?
Upload forms nearly always check file size, not page size. If you shrank the page and the form still rejects it, you changed the wrong thing. Compress it instead. Our PDF too big to upload guide and email guide go through typical limits.
The reverse also holds. If a printer wants A4 and your PDF is Letter, compression will not help, and only the page-size steps above apply. Decide which number the other side checks, then change that one.
When is Smol the wrong tool for this?
Smol cannot change page size. It does not edit, split or merge PDFs, so for A4 versus Letter use the print dialog or Ghostscript. For one PDF that needs to be somewhat smaller, Preview’s Reduce File Size is free and already installed.
Smol is for the other half of “resize”: file size. It has five presets, Tiny to Original, which cap the long edge of page images in pixels, not DPI, and it handles a folder of PDFs at once, on your Mac, with nothing uploaded. “Original” still re-encodes, so it is not lossless. The presets explained post has the numbers. The price is $29 once for one Mac, on the buy page. Some PDFs barely shrink, whatever tool you use.
How we checked this
Built a one-page 768 by 768 pt photo PDF, fitted it to A5 and compressed it with Ghostscript 10.07 on an Apple Silicon Mac, then compared byte sizes and MediaBox values. Facts last checked . We make Smol, so treat our claims about it with the same care as any vendor’s, and see our editorial policy.
Resizing a PDF on Mac: common questions
Does changing a PDF to A4 make the file smaller?
Not by itself. In our test, fitting a photo PDF to an A5 page changed the page from 768 by 768 points to 420 by 595 points, but the file stayed within 150 bytes of its original 319,020 bytes. The embedded image was unchanged. To cut megabytes, compress the images.
Can Preview resize PDF pages?
Not directly. Preview exports and compresses PDFs, but the page size change goes through File > Print: choose a Paper Size, turn on Scale to Fit, then use the PDF menu to Save as PDF. Tools > Adjust Size is meant for images, not PDF pages.
What is the easiest way to downsize a PDF on a Mac?
Open it in Preview, choose File > Export, set Quartz Filter to Reduce File Size and save a copy. It takes seconds and costs nothing. The trade-off is one fixed level that can blur images, so check the copy before sending it, and keep the original.
Will resizing a PDF reduce its quality?
Changing page size alone does not touch image data, though scaling the layout can shift margins. Reducing file size does lower quality, because it re-encodes images at a lower resolution or JPEG quality. Compare the copy at full zoom against the original before you send it.
Can Smol change the page size of a PDF?
No. Smol compresses PDFs with five presets from Tiny to Original and converts the first page to PNG or JPG, but it does not edit pages or change paper size. Use the print dialog in Preview, or Ghostscript, for A4 or Letter. Use Smol when the goal is a smaller file.
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