I find that document zoomed at 100% in Adobe Reader doesn't match printout size when "Actual Size" is selected when printing. When I put printed page next to the screen printed text and all other elements are about 10-15% smaller than on screen.

FWIW this is under Windows 7 x64

Is there an explanation for that?

  • Yes there is and it involves Pixels, Pitch, and DPI. Not all Pixels are created equally. Not all Pitches are the same. And finally DPI is usually 72 by default. – MonkeyZeus Nov 5 '13 at 22:01
  • Well then what's the meaning of 100% zoom? Are you saying that under some circumstances the size will actually match? I have 24" 1920 x 1200 LCD monitor, screen fonts are set to Medium - 125%. – Joe Schmoe Nov 5 '13 at 22:08
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    In this case 100% means "a fixed width/height measured in pixels". But pixel's size depends on DPI and various monitors have various DPI. When printing, you're using length units and those are always identical, no matter what printer you use. – gronostaj Nov 5 '13 at 23:46
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    gronostaj: what you said makes sense, but why length units are also not used for screen zoom? – Joe Schmoe Nov 6 '13 at 0:55
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    I guess because you have to know DPI to calculate real world lengths. DPI stands for "dots per inch", or in this case pixels per inch. Divide number of pixels by DPI and you'll get size in inches. The problem is retrieving DPI isn't trivial. You have to take many factors into account, like screen's DPI, system's UI scaling and miscellaneous hardware hacks (for example Retina MacBooks are reporting smaller resolutions to applications and then scales everything appropriately). – gronostaj Nov 6 '13 at 20:44

I have had a lot of trouble with this since I am trying to use an on screen ruler with a PDF.

Easiest way for me to cope with this is to hold up a piece of A4 and adjust zoom (as Fit Width and keep moving sides of the PDF window) until it matches - 82.1% on my current screen and PDF.


If the document is in Portrait mode on a standard 8.5x11 sheet at 72 DPI (Dots Per Inch or Pixels Per Inch) then 100% means 8.5x72=612 pixels wide so it only takes up 612 of your 1920 pixels wide. However PDFs are usually built to scale well so it's probably at 150 or 300 DPI so 150x8.5=1275 pixels at 100% zoom. Think about a 20-inch 1920*1080 monitor vs. a 27-inch 1920*1080 monitor: the physical pixel size in the LCD is different (or the spacing (pitch) between pixels is different).

If you really want to FUBAR some things then mess around with the global Windows DPI setting.

Finally my math courses pay off!


There is a way to fix that. Go to Edit/Preferences, in "Resolution", select "Custom resolution" and enter the value that you need. For example if your document have 10 cm wide and in the screen it shows as 9 cm with a resolution of 110 dpi, you should multiply 110 x 10 and then divide by 9. The result, 122 is the value that you have to put in the resolution. Then when you select "Real size" (100%) the graphic shows at real size. Sorry for my english


This is most likely the page sizing setting with Adobe reader. Change it to 'Actual Size' (within the print dialoge) and you should get everything showing up at the right size.

  • I think settings on Print dialog have nothing to do with on-screen zoom. They only affect print output. – Joe Schmoe Nov 5 '13 at 23:33
  • They don't, but Adobe is shrinking the document before printing it, causing everything to be smaller. – CyberJacob Nov 5 '13 at 23:34

For Windows 7 users, this is very late but I hope this helps: 1. Go to Start >> Devices & Printers, Right-click and Access your Printer's Printing Preferences 2. Look for Scaling Options/group (Mine is in the "ADvanced" tab 3. SEt the Scaling to "Off"


The explanation is that a preview that matches true paper size was not the goal of the software to begin with, or the software is incomplete, because there is no reason software can't calculate a preview perfectly, at least with the assistance of the OS. All monitors nowadays report their true physical dimensions. Query the EDID and it will report back to you accurate physical dimensions (you can also google various utilities that prove it) like this one which will return exactly the dimensions of your screen panel: https://www.nirsoft.net/utils/monitor_info_view.html

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