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Lengthy story here but in short, I followed some tutorials saying that to get an accurate size of your file in Photoshop when using the "print size" option, you divide your screen's current pixel size with the screen's physical horizontal size (in my case 1920px / 52,8 cm = 36.3636...). then you enter it under the menu "screen resolution" and in my case changed the unit to centimeters instead of inches.

After changed settings I start a new A4 sized document (international paper) and use "print size" on it. And when holding an A4 paper (210mm in length) against the screen, the Photoshop file's length is actually 207mm. Ok, so I tried to make minor adjustments with the decimals (from 36,36 up to 36,99) but nothing changes until the number becomes 37...then the Photoshop file suddenly decides to change size and jumps up to 213mm instead!! Why? The setting allows 3 digit after the decimal...why can't it use them for minor adjustments??

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    You can't have ".363" of a pixel. Pixels must be whole integers.
    – Scott
    Jun 30, 2019 at 17:07
  • @Scott, yes pixels must be integers, but resolution can have decimals. For example if I make a 300 pixels per inch document and switch to pixels per centimeter I get 118,11 ppc.
    – Wolff
    Jun 30, 2019 at 17:22
  • I don't quite understand what you are trying to achieve (besides the fact that you want Photoshop to show a print document at its actual size). The setting you are changing (Preferences > Units & Rulers > New Document Preset Resolutions > Screen Resolution) only affects the resolution of new screen documents. You are creating a print document. And no matter what the resolution of a document is, 100% zoom will still just show 1 pixels of the document as 1 pixel on the screen. Which zoom are you at when measuring the A4 on the screen?
    – Wolff
    Jun 30, 2019 at 17:27
  • In other words: If you are creating an A4 document, you must be trying to create a print document. The resolution of a print document shouldn't be defined to make the document be at scale on your screen. It should be made at the resolution you want to print. Often 300 ppi. So there might be some misunderstanding here?
    – Wolff
    Jun 30, 2019 at 17:30
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    I don't know much about 3D print and i might be wrong, but I don't think that a pixel based application like Photoshop is the right tool. It's meant for creating flat 2D images. How will you get depth? By adding layers? I work with print and I only use Photoshop for editing images and drawings. Then I place them in InDesign/Illustrator which are vector based applications where you have much more control over actual physical size. Changing the resolution of your artwork to force it to be displayed to scale on your specific screen does not make it any more accurate.
    – Wolff
    Jun 30, 2019 at 18:09

1 Answer 1

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To get the Print Size functionality to show the physical size of a print document on screen, follow these steps:

  1. Let w be the width of your screen in cm (obviously you need to measure this with a ruler).

  2. Let x be the width of your screen in pixels (find this in your display settings)

  3. Screen resolution = x / w. Round the value to the nearest two decimal places. This should be accurate enough.

  4. Create a new print document using the print presets in Photoshop, something like an A4 sheet will do. Make sure you set the units to centimetres, and the resolution to 118.11 pixels per centimetre (equivalent to 300ppi).

  5. Go into Preferences > Units and Rulers, set the screen resolution you calculated in step 3, in pixels per centimetre. The print resolution setting should be 118.11 pixels per centimetre.

Now try View > Print Size. Then, with a ruler, measure the width of the sheet on screen. It should be 21cm.

Note: for consistency and to avoid confusion I made all measurements metric, however you can also use imperial measurements if you want. It makes no difference.

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