I have this PDF image of a map with a scale of 1:300. How do I obtain the real length of the object precisely, since it can be zoomed in and out?

Let's just say that I want to calculate the length of this Storage room

enter image description here

From what I have been researching, it seems I need to have the DPI of the image. After I have the DPI what do I have to do to get the length?

Will it give me the 1:300 scale if I print the image?

  • The physical page size of the PDF is fixed. The size of this storage room can be expressed as a fraction of the total page (at any size), and the real page size will give you the 'real' scaled size. Then it's times 300 that.
    – Jongware
    Commented Apr 9, 2016 at 17:12
  • Related: Given one exact measurement, how can I use it to measure the rest?
    – Dom
    Commented Apr 11, 2016 at 12:10

1 Answer 1


You may be over-thinking this. If the scale is 1:300, all you need to do is multiply the current dimension you want to calculate by 300.

For instance if the storage room is 20mm wide:

2cm × 300 = 600cm = 6m

Your storage room is 6m wide.

If you were only capable of measuring in pixels, you would need to know the PPI of the image to calculate the correct physical measurement, you can however measure physical distances in PDFs relatively easy, that depends on the software you are using though.

In Adobe Acrobat and Adobe Reader, for example, there are measuring tools.

Acrobat measure tools

Use the measuring tools to measure distances and areas of objects in PDF documents. The measuring tools are useful for showing the distances and areas associated with objects in a form or computer-aided design (CAD) drawing.

With the scale options of the measuring tools in Acrobat or Reader you won't even have to calculate the measurements, just input the correct scale and the tool will show you the real-life dimensions. Easy.

  • Thank you for your reply and I am very sorry for the late reply. How do i get the "2cm" that you told me above exactly?
    – Adam
    Commented Apr 10, 2016 at 0:34
  • 20mm = 2cm. If you use the measurement tools in Acrobat (or equivalent in whatever other software) you shouldn't need to worry about any of that though.
    – Cai
    Commented Apr 10, 2016 at 0:38
  • No problem. Glad to help :)
    – Cai
    Commented Apr 10, 2016 at 0:49

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